Mobile Home Service Conductors

[JMCDONALD70]

I have just recently attained my ICC certification for electrical inspector and hope to be starting new job soon. I have been doing lots of research in the 2017 NEC and the IRC. My question relates to mobile home service conductor sizing. After the meter if one uses a Mobile Home disconnect with the usual 4 circuits, and let's say they come out of there to get the well pump and the outside condenser. Now let's say this is a 200 amp service. From the disconnect into the mobile home wouldn't you be required to use 3/0 copper which would make your incoming service conductors 3/0 since no feeder conductor can be larger than incoming service conductor. It seems to me you can't use the 83 percent here because the disconnect with the circuits. Everyone around here uses 2/0 in this example. Thanks

 

[ptonsparky]

There is nothing that prohibits feeders larger than the incoming service. Fact is we do it frequently. Not residential, but Ag. VD. I would ask for your code reference.

2020 NEC 310.12(C) is new.

 

[LarryFine]

From the disconnect into the mobile home wouldn't you be required to use 3/0 copper which would make your incoming service conductors 3/0 since no feeder conductor can be larger than incoming service conductor.

You misread. They're not required to be larger, but they may be.

 

[Greentagger]

If the 2/0 does not supply the entire load you are obligated by 310.15(B)(7)(2) to protect it at it’s ampacity per table 310.15(B)(16) which 2/0 copper next standard size over current protection device is 175A.

 

[ptonsparky]

Doesn't it say "entire load associated with a one family dwelling"? I would say that the well and A/C unit are associated with a single family dwelling. 2/0 cu is good for a 200 amp residential service. 310.15(B)(7)(3). The feeder to the dwelling is not required to be larger than 310.15(B)(7)(1)or(2).

2/0 is good for both the SE and the feeder.

 

[Dsg319]

Doesn't it say "entire load associated with a one family dwelling"? I would say that the well and A/C unit are associated with a single family dwelling. 2/0 cu is good for a 200 amp residential service. 310.15(B)(7)(3). The feeder to the dwelling is not required to be larger than 310.15(B)(7)(1)or(2).

2/0 is good for both the SE and the feeder.

I feel the same way. As if the Conductors know wether there are branch breakers at the main outside and in the distribution panel in the house.

 

[JMCDONALD70]

Ok, I think I got it.
Feeder conductors for individual dwelling units or mobile homes needn't be larger than service conductors, which are sized by 310.15(B)(7).
So, if the service conductors for the 200 amp service are sized by the 83 percent rule, then if fact 2/0 is acceptable as both the service conductors and feeder.

 

[Greentagger]

If the well and ac are on different branch breakers than the feeder , then that feeder is no longer serving the entire load. The service conductors are supplying the entire load but the feeder 2/0 is not. It is required to be protected at 175A.

 

[ptonsparky]

The 2/0 SE is feeding the entire load associated with a single family dwelling. The ampacity of the feeder to the dwelling is not required to be larger than the SE. It isn’t. It’s he same.

You are telling me I can put the well and A/C in the house panel and a 2/0 is good for 200 amp, but if I move them to an exterior SE Panel the 2/0 is no longer adequate just because I moved the two breakers. No other changes.

It really doesn’t matter if trailer house or not, the same rule would apply.

 

[Greentagger]

Yes, that’s the gist of it.

 

[david]

If the well and ac are on different branch breakers than the feeder , then that feeder is no longer serving the entire load. The service conductors are supplying the entire load but the feeder 2/0 is not. It is required to be protected at 175A.

310.15(B) (7) (3) supplying the entire load is not mentioned in (3)

that was already established for the service conductors in (1)

Since the feeder in (3) is supplying a load already allowed for the service conductors in (1) the feeder need not be sized any larger than the service conductors

 

[david]

I have just recently attained my ICC certification for electrical inspector and hope to be starting new job soon. I have been doing lots of research in the 2017 NEC and the IRC. My question relates to mobile home service conductor sizing. After the meter if one uses a Mobile Home disconnect with the usual 4 circuits, and let's say they come out of there to get the well pump and the outside condenser. Now let's say this is a 200 amp service. From the disconnect into the mobile home wouldn't you be required to use 3/0 copper which would make your incoming service conductors 3/0 since no feeder conductor can be larger than incoming service conductor. It seems to me you can't use the 83 percent here because the disconnect with the circuits. Everyone around here uses 2/0 in this example. Thanks

Is 2/0 copper acceptable for the feeder size for a 200 amp manufactured home. Probably not but maybe yes maybe no.

Can you even add a ac unit or a pump to a manufactured home 2/0 service?

Here is an example to consider

 

[ptonsparky]

Is 2/0 copper acceptable for the feeder size for a 200 amp manufactured home. Probably not but maybe yes maybe no.

Can you even add a ac unit or a pump to a manufactured home 2/0 service?

Here is an example to consider View attachment 2555356

Granted the instructions that come with the MH or trailer would take precedence.

 

[Greentagger]

In no case shall feeder be larger than service conductors ******if it meets the conditions of 310.15(B)(7)(2)****** which is the entire load( which it does not, with branch breakers for well and ac). Red tag.

 

[Fred B]

The 2/0 SE is feeding the entire load associated with a single family dwelling. The ampacity of the feeder to the dwelling is not required to be larger than the SE. It isn’t. It’s he same.

You are telling me I can put the well and A/C in the house panel and a 2/0 is good for 200 amp, but if I move them to an exterior SE Panel the 2/0 is no longer adequate just because I moved the two breakers. No other changes.

It really doesn’t matter if trailer house or not, the same rule would apply.

Yes, that’s the gist of it.

Ok, not to try to argue requirements, (code is code) but can someone explain the rationale of why allowed one way but not the other? I was one my father complained about always asking "Why?".

 

[david]

In no case shall feeder be larger than service conductors ******if it meets the conditions of 310.15(B)(7)(2)****** which is the entire load( which it does not, with branch breakers for well and ac). Red tag.

It actually says if a feeder meets that specified in 310.15(B) (1) or (2)

a feeder never has to be larger than the service it is associated with

 

[ptonsparky]

Ok, not to try to argue requirements, (code is code) but can someone explain the rationale of why allowed one way but not the other? I was one my father complained about always asking "Why?".

IMO it serves no purpose.

Ignoring possible mobile home mfg requirements, putting the load at the service panel or in a sub does not change the load. Not one bit.

I can use a 200 amp MB panel with feed through lugs, no additional feeders or branch circuits installed, and use 2/0 for the feeders to the home or trailer. Passes inspection without any 'I would like to see' stipulations.

That is where I feel ....(3) comes into play. By requiring a 175 amp breaker, you are in essence requiring an increase of ampacity of that conductor by requiring it to be 3/0 otherwise.

Hopefully you can follow that train of thought,

 

[JMCDONALD70]

Ok, not to try to argue requirements, (code is code) but can someone explain the rationale of why allowed one way but not the other? I was one my father complained about always asking "Why?".

The way I would inspect this job is as follows. If the SE is 2/0 ungrounded conductors and a number 1 grounded conductor, then I would require the same in the feeder circuit along with a number 6 green for the equipment grounding conductor. The feeder can also be sized so as not to exceed the ampacity of 310.15(B)(7) 1 & 2.

 

[david]

Ok, not to try to argue requirements, (code is code) but can someone explain the rationale of why allowed one way but not the other? I was one my father complained about always asking "Why?".

Load diversity in residential applications sizing takes into consideration that you are likely to have different loads on but not all at one time.

But not every feeder for example a feeder to a shed will not have then same range of loads as the dwelling

 

[Greentagger]

Strange rule, strange language, left to different interpretations. I just can’t get past the language of ”entire load”. That’s what I’ll be hanging my hat on.