NEC, service cable, & equipment grounding conductor

[Ryan@graceelectric]

I have a question that has been bugging me for a while. Table 250.122 states that the equipment grounding conductor size for an overcurrent device of up to 200 Amps is a #4 aluminum. Why, then, does #4/0 SER aluminum cable come with a #2/0 aluminum equipment grounding conductor? I’ve been a master electrician for 20 years and have installed hundreds of services with this type of cable. I have also installed plenty of services in conduit where I have used XHHW AL conductors and ran a #4 aluminum equipment grounding conductor per 250.122 for residential services in the past where an external disconnect was required. This latest code cycle requires external disconnects in most, if not all situations, and we have been running across this apparent equipment grounding conductor sizing discrepancy more frequently, being that the main breaker panel is now wired as a sub panel.

 

[Fred B]

If you are talking about the 4 conductor cable most I've used have been 4/0, 4/0, 2/0, #4. And usually only in stock has been the MHF with additional listings. There is a 4 conductor MHF that is 4/0, 4/0, 4/0, 2/0 but that most time is for 3 phase thus the 2/0 is the grounded (neutral) conductor. If you are referring to the 3 conductor type that 2/0 is also the grounded conductor not grounding conductor.

So it may be in part what your supply house is getting or giving for you to use.

Terminology makes a difference. (Grounded vs Grounding)

 

[Ryan@graceelectric]

The cable that my supply house provides is 4/0, 4/0, 4/0, 2/0. You’re right, that may be specific to the manufacturer or type of cable that they carry in stock. It is not three phase cable because there is a distinct white marking for a neutral on one of the conductors. The equipment grounding conductor is bare. I have always found it odd and was wondering if I was missing something in the requirements for an equipment grounding conductor. I have also had an inspector question my use of a #4 AL equipment grounding conductor for a conduit installation, saying that he has always seen a larger equipment grounding conductor. I referred him to 250.122 and he agreed that a #4 AL was acceptable for a 200 a residential service.

 

[infinity]

Why, then, does #4/0 SER aluminum cable come with a #2/0 aluminum equipment grounding conductor?

As Fred stated often that cable with the intended use as SEC's doesn't have an EGC. It has a reduced size neutral for 3Ø applications. If you're running a 200 amp feeder with aluminum then you're correct according to T250.122 the EGC size is #4 Al.

 

[Dennis Alwon]

To build on what Rob stated. Think of a 3 phase service cable. You have 3 phases and a neutral. That 2/0 is sized so that you have a neutral sized more appropriately in that application. It is bigger than required for a sub feeder on single phase but they are making this cable so that it can have a double function.

 

[electrofelon]

Also, presumably, they are are providing some upsize to cover situations where the EGC must be increased in size such as VD and parallel installations. All the MC feeder cable I use has a larger than minimum EGC.