90A breaker with #4Cu?

[sky jumper]

if I pull #4Cu to a subpanel, can I put a 90A main breaker in it? QO main breakers don't come in 85A. I can't find the section in the code that deals with this (if there is one).

 

[Terry D]

240.4(B) allows you to go up to the next standard size overcurrent device. Table 240.6(A) lists the standard sizes. This is from the 2017 NEC

 

[mike93lx]

You can put whatever size main you want in the sub as the feeder size is irrelevant. That breaker is just a disconnect.

The breaker in the main which feeds the sub is the one that the size matters on

 

[SlappyWhite]

Why not #3 and 100 amp? 100 amp is more common...

 

[mike93lx]

Why not #3 and 100 amp? 100 amp is more common...

In many (most?) applications, that 10a get you nothing useful and costs more money.

 

[Terry D]

You can put whatever size main you want in the sub as the feeder size is irrelevant. That breaker is just a disconnect.

The breaker in the main which feeds the sub is the one that the size matters on

You can put whatever size main you want in the sub as the feeder size is irrelevant. That breaker is just a disconnect.

The breaker in the main which feeds the sub is the one that the size matters on

A main is only required if the sub is in a out building and has more than 6 circuits. OP did not specify the location. Im thinking he is talking about the breaker feeding the sub.

 

[mike93lx]

A main is only required if the sub is in a out building and has more than 6 circuits. OP did not specify the location. Im thinking he is talking about the breaker feeding the sub.

He may be, but the wording definitely points to a main in the subpanel.

Hopefully the OP clarifies

 

[sky jumper]

sorry, yes I'm talking about the main breaker in a subpanel in an attached garage. while I think technically I don't need a main breaker, I'm going to use one anyway since the main panel is in the basement on the other side of house... but the same question applies to the double pole breaker feeding it, I think?

as for why not #3? because I can't fit it in the existing conduits that I'm planning to use for this. #4 I can with some rearranging of existing conductors. I'd rather not have to run new 1" EMT all the way though the house if I can avoid it.

while I'm at it... I also installed a generator feed on the main panel via interlock and used #8 Cu. while I currently have a 30A generator (and 30A back-feed breaker) the reason I pulled #8 is to allow for a future 50A generator should I ever get a new one. but is #8 enough for a 50A generator feed? I understand #8 is not enough for continuous 50A load, but is a generator considered continuous?

 

[mike93lx]

sorry, yes I'm talking about the main breaker in a subpanel in an attached garage. while I think technically I don't need a main breaker, I'm going to use one anyway since the main panel is in the basement on the other side of house... but the same question applies to the double pole breaker feeding it, I think?

I think having a main breaker in the sub is smart.

But that breaker size doesn't matter, as I mentioned. Just grab a main breaker panel that has the spaces you need/want and use whatever it comes with. Could be 100, 125, 200, or something else.

The breaker feeding it needs to be sized to the wire, which Terry addressed. You can also go smaller if you want. If a 60a might be enough, that is a size that is often way, way cheaper

The generator being continuous doesn't matter, it is what is connected to that. Is the #8 individual conductors in conduit or is it NM cable?

 

[sky jumper]

The generator being continuous doesn't matter, it is what is connected to that. Is the #8 individual conductors in conduit or is it NM cable?

it's separate conductors in 3/4" metal conduit. it'll being running the whole house, which is not at all continuous. seems to vary from about 15A to a little over 30 depending on if the well pump is running at the same time as the furnaces, etc.

as for 240.4(B).... if I'm reading this correctly, I can go with a 90A breaker to feed the subpanel with #4 if there's only hardwired loads and no more than one receptacle for plug-in loads. did I get that right? this subpanel will be used for a 240V garage heater and future EV charger(s), so yeah they will all be hardwired. now what some future owner might add to it is their issue to work out, right?

 

[mike93lx]

it's separate conductors in 3/4" metal conduit. it'll being running the whole house, which is not at all continuous. seems to vary from about 15A to a little over 30 depending on if the well pump is running at the same time as the furnaces, etc.

as for 240.4(B).... if I'm reading this correctly, I can go with a 90A breaker to feed the subpanel with #4 if there's only hardwired loads and no more than one receptacle for plug-in loads. did I get that right? this subpanel will be used for a 240V garage heater and future EV charger(s), so yeah they will all be hardwired. now what some future owner might add to it is their issue to work out, right?

I'm not an electrician, so I'll leave a confirmation to one of the guys here.

If 30a is getting it done, I'd leave it alone and not worry. I do think that #8nin conduit gets you a 50a rating, but again, I'm not a sparky.

And yes, as long as you do it right on your end now, what the next guy does is his problem, not yours

 

[wyliesdiesels]

yes #8 THWN in pipe is good for 50a