Customers call Nassau National Cable every week asking which of these four cables to run for a 200 amp service, a subpanel feeder, or a run out to a detached garage, prompting us to create a guide on the topic.

SEU and URD when double-rated as USE-2 are service entrance cables, whereas MC is a feeder cable. SER is a unique cable that works as both service entrance and feeder.

This guide starts with a clear service entrance vs. feeder distinction. Then it walks through what each cable is, where it's allowed, where it's banned, and how to answer the questions that come up during a real install. Let's proceed.

Service Entrance vs Feeder: Start Here

The difference between service-entrance wiring and feeder wiring comes down to which side of the main service disconnect the conductors are on.

A service entrance conductor runs from the utility connection point to the service disconnect. That means from the weatherhead down to the meter, and from the meter to the main breaker in the panel. Everything on the utility side of the main disconnect is service entrance.

A feeder carries power from the main disconnect to a downstream panel. A run from your main panel to a subpanel in the garage is a feeder. A run from a main disconnect in a detached building back to a subpanel in the house is a feeder.

The key difference is grounding. Before the main disconnect, the neutral also serves as the grounding path. After it, feeders need four conductors: two hots, an insulated neutral, and a separate equipment ground.

• SEU is primarily a service-entrance cable because its bare/concentric neutral is not separated from the grounding path.

• MC cable is commonly used for feeder runs when it contains the required insulated conductors and equipment grounding path.

• URD can be used for service or feeder applications only when the individual conductors carry the appropriate listing/rating for that installation (RHW-2/USE-2).

• SER can serve both service-entrance and feeder applications because it includes two hots, an insulated neutral, and a separate equipment grounding conductor.

Service Entrance Rated vs Non Service Entrance Rated

"Service entrance rated" means the cable is listed and marked for use as service entrance conductors under NEC Article 338. Type SE cable, in its SER and SEU forms, is service entrance rated. Type USE and USE-2 are the underground counterparts.

URD is a utility construction manufactured to ICEA and RUS specifications. Straight URD marked only "URD" is generally intended for utility-owned distribution. When marked URD/USE-2, it can also be used for customer-owned underground service-entrance applications. If it also carries an RHW-2 rating, it can continue into wet or dry raceways, including indoors where permitted.

Always check the cable print. If it is not marked USE or USE-2, do not specify it as customer-owned service-entrance cable. URD that lacks a service-entrance rating may still be used for underground feeder or distribution runs if its conductors are properly listed.

Nassau National Cable sells RHH/RHW-2/USE-2-rated conductors for direct burial, service-entrance, and broader raceway applications.

Non-service-entrance-rated cables include MC, NM, UF, and standard building wire. These cannot be used as service-entrance conductors on the line side of the main disconnect, except under narrow exceptions.

The NEC addresses a few edge cases customers ask about:

• Can Type UF cable be used as service entrance cable? No, not on the load-side interior wiring, and not on the service-entrance run itself. UF is a feeder and branch circuit cable for wet locations and direct burial, per NEC 340. It is not listed for service entrance use.

• Is Type NMC suitable for use as service entrance cable? No. NMC is a nonmetallic sheathed cable for corrosive and damp interior locations. NEC 334 does not permit it as service entrance.

If a cable is not marked SE, SER, SEU, USE, or USE-2, treat it as non-service entrance rated for service work.

Types of Service Entrance Cable

The main types of service entrance cable are:

• Type SE (Style R), or SER. Round jacket, insulated neutral, separate insulated or bare grounding conductor. Used above ground for service entrance and for interior feeders.

• Type SE (Style U), or SEU. Flat oval jacket, concentric bare neutral wrapped around two insulated phase conductors. Used for the exterior run from the weatherhead to the meter and from the meter to the main disconnect.

• Type USE and USE-2. Underground Service Entrance. Direct burial rated. Used for the buried lateral from a padmount transformer or utility source to the meter.

• Type URD. Underground Residential Distribution. Utility-style secondary cable, twisted duplex or triplex, XLPE insulated, no overall jacket. Direct buried. Widely stocked as a secondary service cable and often specified interchangeably with USE for residential laterals when dual rated.

Aerial service entrance cable types are typically SEU on the drop side of the weatherhead. The utility service drop itself is a triplex overhead conductor, a separate product category from SE cable.

Type SE service entrance cable is for above ground use. When used as a service entrance cable, type SE is installed exposed on the exterior wall from the weatherhead to the meter and from the meter to the main disconnect. It is not rated for direct burial in any form.

URD Cable

URD (Underground Residential Distribution) is a utility-grade secondary cable. The construction is two, three, or four aluminium conductors twisted together with XLPE insulation, rated at 90 degrees C wet and dry, sunlight-resistant, and direct-burial rated.

For customer-owned installations, check the conductor print. USE-2-rated URD is listed for underground service entrance and direct burial. If the conductors are also marked RHH/RHW-2, they can be used in raceways and wet or dry locations where permitted.

URD is used for:

• The underground lateral from a padmount transformer or handhole to the meter base on the house

• Secondary distribution runs by the utility

• Underground primary distribution at 15, 25, or 35 kV in shielded MV constructions

Can URD cable be used for a subpanel feeder? Not as manufactured. URD has no separate equipment grounding conductor. A feeder to a subpanel needs a separate insulated neutral and a separate EGC. If you pull individual XHHW-2 conductors through conduit, that is a different install. The URD assembly itself is not a feeder cable.

Can URD cable be used for a detached subpanel? Same answer. Feeders to a detached building require a separate EGC per NEC 250.32. URD does not provide one.

Can I use URD cable on an overhead service? No. URD is not rated for aerial installation. It is a direct burial secondary. For overhead service, the utility uses triplex overhead conductor, and the customer side uses SEU from the weatherhead down.

Can I use URD cable above ground in PVC? URD is rated for direct burial and sunlight exposure. Running it through PVC conduit above ground is not the intended application, and the XLPE conductors are typically not marked for use in raceway as a bundled assembly. If the run is above ground, spec individual XHHW-2 conductors or SER instead. Some jurisdictions allow short PVC transitions from underground to the meter, and utility rules on the service lateral often govern that stretch.

SER Cable

SER (Service Entrance, Style R) is a round jacketed cable with two or three insulated phase conductors, an insulated neutral, and a separate insulated or bare grounding conductor. Conductors are XHHW-2, rated at 90 °C wet and dry. Available in copper or aluminum. Common sizes for 200-amp work are 4/0-4/0-2/0-4 aluminum or 2/0-2/0-1-4 copper.

Type SER cable may be used for:

• Service entrance conductors from the meter to the main disconnect

• Interior feeders from the main panel to a subpanel

• Feeders to detached buildings when run in conduit or with proper protection

• Branch circuits when sized appropriately

Type SER cable uses not permitted:

• Direct burial (unless specifically marked and listed for it)

• Locations subject to physical damage without protection

• Where the ampacity table 310.16 is exceeded

Is SER cable rated for outdoor use? Yes, above ground. The PVC jacket is sunlight resistant. Support is required every 4.5 feet per NEC 338.10 and within 12 inches of every termination.

Can you use SER cable indoors? Yes. NEC 338.10(B) allows SER as an interior feeder and branch circuit. This is where SER earns its keep on residential and light-commercial jobs. When used as an interior wiring method, SER installed in thermal insulation is limited to the 60-degree C ampacity column per 338.10(B)(4)(a).

Can SER cable be used underground? No, not direct buried. Standard SER is not listed for direct burial. If the run must go through a wet or below grade location, pull individual conductors through conduit instead, or spec USE.

Can SER cable be used in conduit? Yes. SER is commonly pulled through PVC or EMT for exterior exposed runs, wall penetrations, and transitions. Watch the conduit fill tables in NEC Chapter 9, because SER is a multiconductor cable and the outside diameter drives the fill calculation.

Can I use SER cable for a subpanel? Yes, this is one of its primary uses. SER carries the two hots, insulated neutral, and separate EGC that a subpanel feeder needs.

Can I use SER cable in a warehouse? For interior feeders and branch circuits in a warehouse, SER is permitted when the installation complies with Article 338 and the support requirements. In many warehouse builds, MC is a better choice because the metal armor provides physical protection without needing conduit.

SEU Cable

SEU (Service Entrance, Style U) is the flat oval cousin of SER. Two insulated phase conductors sit side by side, with a concentric bare neutral wrapped around them, all encased in a PVC jacket.

When used as a service entrance cable, type SEU is the exterior run from the weatherhead down to the meter and from the meter over to the main disconnect. That is essentially its only job.

SEU uses:

• Service entrance from weatherhead to meter

• Service entrance from meter to main disconnect

• 120/240V single-phase residential and small commercial services

SEU uses not permitted:

• Interior feeder to a subpanel (the concentric bare neutral is a grounded conductor, not an EGC, and past the main bonding jumper you need a separate EGC)

• Any application where a separate equipment grounding conductor is required

• Direct burial

There is a narrow exception in NEC 338.10(B)(4). SEU can be used as an interior wiring method if the uninsulated conductor is used only as an equipment grounding conductor, not as a neutral. That is unusual in residential work and rarely worth the confusion.

Should I Use SER or SEU for a Service Upgrade

Both are Type SE cable. The choice depends on where the main disconnect sits and how many conductors the run needs to carry.

Use SEU when:

• The meter is on the exterior wall and feeds directly into a main breaker panel just inside the wall

• The service is 120/240V single phase with no separate equipment grounding conductor required on the utility side of the main disconnect

• The exterior run from weatherhead to meter is exposed on the wall.

SEU is the traditional service upgrade cable for straight residential jobs. Its concentric bare neutral serves as the grounded conductor on the line side of the main disconnect, as the code allows for service-entrance conductors.

Use SER when:

• The service upgrade includes a meter main combo (meter with a main breaker at the exterior) feeding an interior panel that is now a subpanel by definition.

• The run from the meter main to the interior panel is a feeder and needs a separate insulated neutral plus a separate EGC.

• The interior panel is more than a short conductor length from the meter, and local code requires a load side wiring method.

• The AHJ requires four-wire construction past the meter.

On many modern service upgrades, the main disconnect is installed outside at the meter. In that setup, SEU runs from the weatherhead to the meter/main, and SER runs from the outdoor main disconnect to the interior panel, which is now a subpanel. SER is needed for that feeder because it provides two hots, an insulated neutral, and a separate ground.

If the main disconnect remains inside the house at the first panel, the wiring is still service entrance up to that point. In that case, the SEU can run from the weatherhead to the meter, then to the indoor main panel.

MC Cable

MC (Metal-Clad) is commonly used for interior feeder and branch-circuit wiring. It contains insulated THHN/THWN-2 conductors within interlocking aluminium armour, typically with a separate equipment-grounding conductor. Standard unjacketed MC is for dry locations; jacketed MC constructions may also be listed for wet locations or direct burial.

Best use for MC cable:

• Branch circuits in commercial and industrial buildings

• Feeders inside buildings where conduit is not required

• Exposed runs in warehouses, retail, and light industrial

• Wet locations when the cable is listed for wet use (look for a corrosion-resistant jacket over the armor)

8 uses permitted for MC cable under NEC 330.10:

1. Services (with listed types, only from the meter to the main service disconnect), feeders, and branch circuits

2. Power, lighting, control, and signal circuits

3. Indoors or outdoors

4. Exposed or concealed

5. Direct buried when identified for the use

6. In cable tray

7. In any approved raceway

8. In hazardous locations when specifically listed (MC-HL)

NEC MC cable uses not permitted: where subject to physical damage without protection, in destructive corrosive conditions unless jacketed for it, and as a service entrance conductor unless the specific MC construction is listed for service entrance use. Standard MC is not.

Type MC cable may not be used in most wet locations without a corrosion resistant jacket, in direct burial applications unless specifically identified, or in hazardous locations unless the specific MC-HL variant is used.

Can MC cable be used in damp locations? Yes, standard MC is rated for damp locations. Wet locations require MC with an impervious moisture barrier or a PVC jacket.

Can MC cable be used outdoors? With the right listing, yes. PVC jacketed MC is the outdoor choice. Bare armor MC left outside will corrode.

PVC coated MC cable uses permitted: wet locations, outdoors, direct burial when marked for it, food processing plants, car washes, and other corrosive environments.

Can I use MC cable instead of conduit? In most commercial branch circuit and feeder applications, yes. MC is often faster to install than pipe and wire. It cannot replace conduit where the NEC specifically requires a raceway, such as some hazardous location classifications or where physical protection is mandated.

What is blue MC cable used for? The blue jacket is a manufacturer color code that usually indicates healthcare or hospital grade MC (MC-HCF), which has an insulated equipment grounding conductor in addition to the armor and bonding strip. Verify the print on the cable, because color coding is not standardized across manufacturers.

200 Amp Service and Feeder Sizing

A 200-amp service serves most residential and light commercial jobs. Here is how the cable choice usually breaks down.

200 amp service cable, incoming from utility:

• Underground lateral: URD/USE-2, 4/0-4/0-2/0 aluminum, direct buried

• Overhead service drop: utility triplex, then 4/0-4/0-2/0 aluminum SEU from weatherhead down.

• 200 amp wire size for copper service: 2/0-2/0-2/0 copper SEU

200 amp feeder cable, main panel to subpanel:

• Standard interior feeder: SER 4/0-4/0-2/0-4 aluminum or SER 2/0-2/0-2/0-1 copper

• Long runs to a detached building: individual XHHW-2 conductors in PVC conduit, sized for voltage drop

• Warehouse or commercial interior: MC or individual conductors in EMT

NEC 310.12 allows the 83 percent rule for dwelling services and main power feeders, which is what lets 4/0 aluminum SEU carry 200 amps for a house even though 4/0 aluminum in a standard raceway is rated at 180 amps in the 75 degree C column. That rule applies only to the service and the main power feeder to the dwelling, not to every subpanel feeder in the house.

200 amp underground feeder cable from the main panel out to a detached garage subpanel: pull four individual XHHW-2 conductors (two hots, neutral, ground) through PVC conduit. This is the standard method and gives you a separate EGC as required by NEC 250.32.

Aluminum entrance cable for 200 amp feed: 3/0 copper MC or 250 kcmil aluminum MC, or the same-size individual conductors in EMT, for a 200A feeder.

200 amp 3-phase feeder: If a neutral is required, the feeder needs three phase conductors, a neutral, and a ground. Aluminum SER can be 250-250-250-250-3/0, while a typical copper MC feeder would use four 3/0 copper MC conductors plus a 6 AWG copper ground. In commercial buildings, MC or individual conductors in EMT are more common than SER for three-phase feeders.

URD vs SER vs SEU: How to Pick

URD vs SER cable is a service side vs load side question. URD is the buried lateral. SER is the feeder from the main disconnect to a subpanel. They rarely substitute for each other.

SER vs URD cable for a detached building feeder: SER pulled in conduit if the run is short, individual XHHW-2 in PVC if the run is long or buried. URD is not the right cable because it lacks a separate EGC.

SER vs SEU vs URD in one sentence each:

• SER: interior feeders and above ground service entrance where a separate EGC is required or preferred

• SEU: exterior service entrance from weatherhead to meter and meter to main disconnect

• URD: buried service lateral from the utility source to the meter

Transitioning SER to URD for an Underground Run

The scenario: SER comes down from the main panel or meter main, and the run has to go underground to reach a detached building or a distant meter location.

You have three ways to make the transition from SER to URD:

Option 1: Transition in a weatherproof junction box. Land the SER conductors in a NEMA 3R junction box mounted on the wall at ground level. Land the URD conductors in the same box. Splice conductor to conductor using listed connectors sized for the wire. This is the cleanest inspection-accessible method. The box has to remain accessible per NEC 314.29. Do not bury the junction box.

Option 2: Sleeve the SER in conduit down to below grade and switch to URD underground. Run PVC conduit from the panel or meter down the wall, into the ground, and out to a below grade transition point in a listed underground pull box or splice kit. This is more work and creates a buried splice, which many AHJs will not accept unless the splice enclosure is rated for direct burial and submersion.

Option 3 (recommended in most cases): Skip SER entirely and pull individual XHHW-2 conductors through PVC conduit. Run PVC from the panel or meter down the wall and underground to the destination. Pull two hots, an insulated neutral, and a separate EGC as individual XHHW-2 conductors. No splice, no transition, no code question. This is what most inspectors want to see on a feeder to a detached building.

For a 200-amp feeder running underground to a detached building, Option 3 is the standard installation. Expect 3/0 copper or 250 kcmil aluminum XHHW-2 conductors for a typical 200A feeder using the 75°C column of NEC Table 310.16, plus a properly sized equipment grounding conductor. Check voltage drop on longer runs, especially beyond about 100 feet.

If the underground portion is the utility service lateral on the line side of the meter, URD or USE-2 can run directly to the meter base. No separate transition or splice is needed: the utility conductors terminate on the meter's line-side lugs, and SEU, SER, or another permitted service-entrance wiring method leaves from the load-side lugs toward the service disconnect.

Transitioning from Service Entrance to MC

Most commercial and industrial service upgrades end with service entrance cable landing at the main disconnect, and MC feeders leaving the load side of that disconnect to serve subpanels and branch circuits.

The transition point is the main disconnect enclosure. SEU or SER lands on the line side lugs of the main breaker. MC leaves from the load side lugs through listed MC connectors installed in knockouts on the enclosure. The service entrance and the MC feeder never occupy the same raceway or cable.

Three rules to keep the transition clean:

1. Use listed MC connectors at every enclosure penetration. Anti-short bushings on the armor, proper strain relief, and correct connector type for wet or dry location.

2. Do not splice service entrance conductors to MC feeders inside the meter socket. The meter socket is in the service compartment and is not intended for load-side splices. Land at the main disconnect instead.

3. Verify the MC has an equipment grounding path. Standard MC uses the armor plus the bonding strip as the EGC. That combination is recognised as an EGC only when the MC is installed with listed fittings and the bonding strip is properly terminated. If the panel is a subpanel, the EGC in the MC has to land on the ground bus, not the neutral bus.

For a 200 amp feeder cable from a service disconnect to a subpanel using MC, spec MC in 4/0-4/0-2/0 aluminum or 2/0-2/0-2/0 copper with an appropriately sized EGC per NEC 250.122. Confirm the specific MC construction includes an insulated EGC if the run is long or the AHJ requires it. Standard MC with armor and bonding strip only satisfies most inspections, but healthcare and some industrial specs require MC-HCF or a construction with a separate insulated EGC.

Cable from Meter to Panel

The cable from the meter to the main disconnect is service entrance conductors. Options:

• SEU for a straight exterior run down the wall to a disconnect mounted next to the meter

• SER if the run enters the building and travels through interior wall space to reach the main panel, or if the AHJ requires the separate EGC construction

• Individual conductors in conduit for longer or protected runs

The main disconnect must be located per NEC 230.70, which limits the length of unfused service entrance conductors inside the building. Local amendments often tighten this further. Check with the AHJ before you spec a long interior run of SEU.

Direct Burial

When customers search for direct burial or direct burial wire, the answer for residential and light commercial is one of three cables:

• URD for the utility side underground service lateral

• USE-2/URD where the spec calls for a listed service entrance underground cable

• UF for feeder and branch circuit direct burial applications like a run out to a detached garage or a landscape lighting circuit

SER, SEU, MC, and standard building wire are not direct burial rated. If a buried run is unavoidable, use conduit and pull individual XHHW-2 or THWN-2 conductors.

Quick Reference for the Most Common Jobs

• Underground service from padmount transformer to meter: URD/USE-2

• Overhead service, weatherhead to meter to main disconnect: SEU

• Meter main to interior subpanel: SER

• Main panel to subpanel inside the house: SER

• Main panel to subpanel in a detached garage: individual XHHW-2 in PVC, sized for voltage drop, with a separate EGC

• Warehouse or commercial branch circuits: MC

• Wet or corrosive commercial location: PVC jacketed MC

Common Mix Ups

The SEU vs SER confusion sends more cable back for return than any other single mistake. If the cable extends beyond the main disconnect, it needs a separate insulated neutral and a separate EGC. That is SER, not SEU.

The URD as feeder mistake is the second most common. The bare concentric neutral in URD is not an equipment grounding conductor. A subpanel needs both a neutral and a ground. URD gives you one wire that does both jobs, which is fine on the utility side of the main disconnect but not fine anywhere else.

The MC as service entrance mistake is the third. Standard MC is not a service entrance cable. Only specifically listed MC constructions can be used as service entrance conductors, and they are not the same product you order for interior branch circuits.

Nassau National Cable stocks URD, SER, SEU, and MC in the common residential and commercial sizes. If you are unsure which construction fits the job, call before you cut. It is faster than replacing the run after the inspector red tags it.