wire size

[Dave Maxwell]

Menards has big sale going on now. What size wire do I need for a 200 amp run from house to shop? Over 200 foot. Running off a 100 amp breaker until I get new service. Might not be for years. Just want big enough for the day o do decide

 

[Speedy Petey]

Why in the world would you need a 200A feeder to a home shop???

 

[Dave Maxwell]

Ran 60late are old one with no problem. Going to have 100i here and may never upgrade to 200. Welders and compressor. But they don't run at the same time though

 

[Speedy Petey]

Point is, there is a BIG price difference in the wire, and terminating wire rated for 200A in 100A equipment WILL prove challenging.

 

[Dave Maxwell]

Good point. Mt house has 150 service. I have a new 100amp box from a previous plan at old house
to what size for 100 tthen

 

[Speedy Petey]

Since this is on a residential property most inspectors will allow #2al or #4cu.
If not then either #1 or 1/0al, or #3 or #2cu, depending on the setting an cable/conductors used.

 

[MrMark]

If inspectors are allowing that they should be fired.

The correct answer without regard to Vdrop is #2 Cu NMB or perhaps #3 THHN (although I question this in most settings).

 

[RPH]

So nmb and thhn are rated for wet locations?
Uf or thwn is rated for wet.

 

[MrMark]

No, no on the nmb. Can't run that in conduit underground. Just throwing the nmb out there for generic info. Thhn/Thwn in conduit or some other option rated for wet.

 

[Speedy Petey]

If inspectors are allowing that they should be fired.

Would you elaborate?

The correct answer without regard to Vdrop is #2 Cu NMB or perhaps #3 THHN (although I question this in most settings).

May I ask WHY you would question this? It is code correct.

 

[IONH]

Good point. Mt house has 150 service. I have a new 100amp box from a previous plan at old house
to what size for 100 tthen

Just because you have a 100 amp spare breaker box available doesn't mean you have to run 100 amp to it. Replace the main breaker with a 60 amp or whatever is equivalent size wire you ran to it. Don't forget to properly size the feeder breaker in the main panel.

 

[Dave Maxwell]

Don't have any wire yet. Will have a plasma cam soon also. Want to run it and my welder and possibly compressor at same time

 

[MrMark]

Would you elaborate?





May I ask WHY you would question this? It is code correct.

Yes, the garage feeder does not carry 100 percent of the diversified load of the service, thus it is ineligible for special treatment aka undersized wires.

Not so sure. It depends on the temperature rating of the devices it connects. Section 110.14(c). It would only be valid for 75 degree terminals. 2 cu would be required for 100 amps for 60 degree terminals.

 

[mrb]

when using bigger wire and a smaller breaker (60a breaker on #2 wire or whatever) you have to keep an eye on the size of the EGC as it must be proportionally increased when compared to the other conductors, and at some ampacities and wire size combinations, it doesnt calculate out correctly.

 

[Dave Maxwell]

What is EGC

 

[mrb]

What is EGC

the "ground" wire

 

[pattenp]

EGC = Equipment Grounding Conductor

 

[Dave Maxwell]

I borrowed the 2011 nec. Hard to find info on it

 

[Speedy Petey]

Yes, the garage feeder does not carry 100 percent of the diversified load of the service, thus it is ineligible for special treatment aka undersized wires.

Regardless, many inspectors DO still allow this for residential sub-panels.
In my area, #2AL is the norm for 100A sub-panels.

Not so sure. It depends on the temperature rating of the devices it connects. Section 110.14(c). It would only be valid for 75 degree terminals. 2 cu would be required for 100 amps for 60 degree terminals.

Hence my statement about it being code correct.

 

[mrb]

Regardless, many inspectors DO still allow this for residential sub-panels.
In my area, #2AL is the norm for 100A sub-panels.

and they dont make you protect it with a 90a breaker?

 

[MrMark]

Regardless, many inspectors DO still allow this for residential sub-panels.
In my area, #2AL is the norm for 100A sub-panels.



Hence my statement about it being code correct.

I wouldn't go by what some uneducated inspector allowed when you knew it was wrong. The NEC is the standard, not what some inspector allows because they are incompetent or mistaken.

 

[Speedy Petey]

I wouldn't go by what some uneducated inspector allowed when you knew it was wrong. The NEC is the standard, not what some inspector allows because they are incompetent or mistaken.

Actually our inspectors are some of the smartest around. We do not have all-in-one inspectors here who need to cover every trade. We use third party electrical-ONLY inspectors.

And it is/was NOT entirely wrong. MANY areas used 310.15(B)(6) for both sub-panels and services. It is all in the interpretation.
Because they allow us to use a 100A feeder breaker instead of a 90 that makes then "incompetent" and "uneducated"?? Come on now.

 

[MrMark]

Aren't you the one always posting how dangerous electrical is and how only licensed electricians should play with it and all this - no doubt because you are a licensed electrician. And, then you come up with this? Clear code violations are acceptable because it's just a little violation? The comments to the relevant section of the 2008 NEC make it absolutely incorrect to do what your great inspectors allow. There is no matter of interpretation.

 

[Speedy Petey]

There is no matter of interpretation.

I disagree.

 

[MrMark]

I disagree.

You disagree@! Based on what? Support your unsupportable position to show how much you know as a licensed electrician.

 

[mrb]

I disagree.

an inspector does not have the legal authority to make code interpretations or exceptions. The Building Official must do it, that is whoever is in charge of the building dept and it must be written to be legal. An inspector allowing or missing a violation does not make the installation legal.

 

[mrb]

And it is/was NOT entirely wrong. MANY areas used 310.15(B)(6) for both sub-panels and services. It is all in the interpretation.

Because they allow us to use a 100A feeder breaker instead of a 90 that makes then "incompetent" and "uneducated"?? Come on now.

310.15(B)(6) is not open to interpretation. The feeder either carries the entire load of a single dwelling unit or it does not. Its black and white.

If an inspector allows you to undersize a feeder, i would consider that incompetent. If the inspector worked with the local building official to grant you an exemption for your undersized feeder, I would consider that inspector to be a professional.

I have a feeling your 3rd party inspectors just dont care as they have no vested interest in the legality of the work they inspect. They (I am making an assumption here) get paid per inspection and want to get through their stops for the day.

Here is what happens when you have such an inspector covering the structural on a component of one of the most expensive private construction projects in the country http://en.wikipedia.org/wiki/The_Harmon

 

[Speedy Petey]

You disagree@! Based on what? Support your unsupportable position to show how much you know as a licensed electrician.

Based on the fact that this is NOT as black and white as you think it is. MANY areas are/were the same as mine with regard to this.
I know quite a bit as a licensed electrician, but you can attempt to discredit me all you want. I don't have to prove myself to the likes of you.

mrb & mark, you're right . I am wrong. That's what you want to hear so there it is, patronizing as it is.

 

[MrMark]

I just want a cite to the language of a section of the NEC to show that this is a matter of interpretation and that it is not as black and white as I think it is.


What's the deal on dual marked breakers termination rating wise: I see every breaker is marked 60/75 - what does this mean? Does it default to 60 when installed in a panelboard with other breakers?

 

[pattenp]

My understanding is breakers are marked as 60/75 simply to make it clear that it’s okay to use either a 60 or 75 degree rated wire connected to the breaker.

I just want a cite to the language of a section of the NEC to show that this is a matter of interpretation and that it is not as black and white as I think it is.


What's the deal on dual marked breakers termination rating wise: I see every breaker is marked 60/75 - what does this mean? Does it default to 60 when installed in a panelboard with other breakers?

 

[MrMark]

My understanding is breakers are marked as 60/75 simply to make it clear that it’s okay to use either a 60 or 75 degree rated wire connected to the breaker.

I seem to remember discussion that whenever a dual marked breaker is put in a panel with any other breakers that it defaults to 60 degree termination. Therefore, for 100 amps or less you basically always have to use the 60 degree column.

Isn't this correct?

Also, in looking at the QO breaker I see a 40 degree marking on the breaker. What is this referring to?

 

[pattenp]

I can't say you're wrong, but I can't find any info that says you're right. Scanning through the NEC I don't see anything that supports your memory. That would mean if I pulled a bunch of circuits using conduit with THHN (75C) wire and had one circuit that used NM (60C) I would have to use the 60C degree rating for sizing all of the circuits. That doesn't seem right to me.

I seem to remember discussion that whenever a dual marked breaker is put in a panel with any other breakers that it defaults to 60 degree termination. Therefore, for 100 amps or less you basically always have to use the 60 degree column.

Isn't this correct?

Also, in looking at the QO breaker I see a 40 degree marking on the breaker. What is this referring to?

 

[mrb]

the 40deg marking is the ambient operating temperature. the 60/75 is the terminal temperature rating, meaning it may be used for wire of the appropriate type and sized based on those ratings consistent with the nec requirements.

 

[Dave Maxwell]

I will be running a 100 amp breaker off house panel. From previous experience I had to trim some of the strand to fit the wire into the breaker. Is this allowed?

 

[pattenp]

NO NO NO. You shouldn't have to trim the wire if you used the correct size wire for 100A.

I will be running a 100 amp breaker off house panel. From previous experience I had to trim some of the strand to fit the wire into the breaker. Is this allowed?

 

[Dave Maxwell]

Will have to find out what wire I'm going to need

 

[MrMark]

the 40deg marking is the ambient operating temperature. the 60/75 is the terminal temperature rating, meaning it may be used for wire of the appropriate type and sized based on those ratings consistent with the nec requirements.

But what about my question on the 60/75 dual marked breakers defaulting to 60 when put in a panel with other dual marked breakers? Do you have any understanding of that situation?

There was a discussion here where some very good members PHR and Charles in Georgia stated that you had to use the 60 degree rating with these dual marked breakers.

 

[Aceman]

Will have to find out what wire I'm going to need

Copper: #3, #8 ground

Aluminum #1, #6 ground. That said, we'll use 1/0 for 100 amp, I've never seen #1 Aluminum around here.

 

[Dave Maxwell]

Thanks everyone for the info.

 

[pattenp]

Dave, I assume you are running this wire in conduit underground. If so, you should consider Mobile Home Feeder. The sizes are limited and 2/0-2/0-2/0-1 or 2/0-2/0-1-4 is what I think you could get to handle the full 100A. The 2/0 will give you up to 135A if needed and it should fit in a 100A breaker.
See this on MHF...

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15


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