We were told our house had 100amp service, but our insurance man says that this is a split 50/60 amp service. I have attached a picture. What do you think? I was told by the inspector that the main wire was 100 amp service. The insurance company won't insure the house and it costs $2000 to fix.

That is a 100A service and there is NOTHING to "fix". Tell your insurance man to stick to insurance!

The only thing he got even close to correct is that it is possibly a split buss panel. It is still a 100A service.

Add to Stan's response for clarity, just in case Radonlady doesn't know what "split buss" means. Hope you don't mind Stan.

A split buss panel is the standard panel construction in a residential service. That simply means that the panel is constructed such that every other breaker contacts the incoming hot of the opposite side. That feature is what allows you to have both 120 volt service and 240 volt service. Each of the incoming hots cables have 120 volts between it and the ground, but are in opposite halfs of the cycle. When one is positive the other is negative. That gives you 240 volts betewwn the two hots. Note in the drawing below that the top half of the double breaker is in contact with the cable on the left and the bottom half is in contact with the cable on the right.

A true split bus panel has two sets of feeder lugs, and are not used much any longer.

See attached photo, and following link:

Split Buss Panels - Electrician Talk - Professional Electrical Contractors Forum

The panel I see in the poster's photo is a standard single phase 120/240 volt panelboard. A clearer photo would help.

HK, I don't mind at all. Problem is TK is correct. What you described is simply a main lug panel.

A split-buss panel is a panel in which the top four or six two-pole breaker are the mains. One of those mains feeds the bottom half of the panel. This breaker is typically called the "lighting main".

I stand corrected. Thanks TK and Stan.

I would like to humbly add a little clarification if I may. And this is coming from a non-electrician so I am more than happy to have my clarification clarified by a pro. It is my understanding that the size of the home's electrical service depends on at least 3 variables.

1) The size of the incoming service entrance conductors (feeder wires). The larger the conductor the more ampacity they have. Copper can safely carry more amperage than aluminum on a same diameter basis.

2) The ampacity of the main breaker. For example, If you have a 100 amp main breaker/fuse and service entrance conductors that can only safely carry 60 amps of power then you have a 60 amp service.

3) The rating of the service panel. The breaker/fuse service panel has a manufacturer's label on it that specifies the maximum main breaker/service entrance conductor for which it is suited.

Typically the smallest of these three variables is the true size of the incoming electric service.

This is the only statement that is true:

Quote:

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Originally Posted by InspectorDan

2) The ampacity of the main breaker.

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Without going into too much detail, according to code in too many ways to go over right now, I can actually have a 100 Amp Service Disconnecting Means (AKA main Breaker), and conductors smaller than 100 amp rated.

I could have a panel that is rated 200 amps but protected by a 100 amp Main Breaker and #4 wire feeding the 100 Amp Main Breaker,

So...

A service rating shall be considered as sized only according to the rating of the Main Breaker.

Therefore, the statement:

Quote:

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Originally Posted by InspectorDan

Typically the smallest of these three variables is the true size of the incoming electric service.

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Is not true.

TK, I have to strongly disagree here.

What you say is true about the equipment, but if someone has a 100A service, and replaces the panel with a 200 for some reason, such as damage, it is STILL a 100A service.
The entrance cable, meter and grounding/bonding are all still sized for 100A.
The main breaker is almost incidental.

"Without going into too much detail, according to code in too many ways to go over right now"

Please go into detail. It's details that make for safe electrical installations.


"I could have a panel that is rated 200 amps but protected by a 100 amp Main Breaker and #4 wire feeding the 100 Amp Main Breaker."

You could NOT have a #4 wire feeding a 100 amp main. It would be unsafe and non-compliant since the conductor could not carry 100 amps of current without overheating.

InspectorDan,

TK is correct. #4 AWG Copper is rated for 100 amps as a service feeder. I believe the code reference is T 310.15 (B) (6).

Quote:

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Originally Posted by stanfortyman

TK, I have to strongly disagree here.

What you say is true about the equipment, but if someone has a 100A service, and replaces the panel with a 200 for some reason, such as damage, it is STILL a 100A service.
The entrance cable, meter and grounding/bonding are all still sized for 100A.
The main breaker is almost incidental.

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Stan, No need for you to strongly disagree, just state your opinion and give your example. Let's just have a informative conversation and exchange ideas.

Of course I agree with your senario, but if that be the case, who ever installed such a service needs to loose their license, as it is not according to code, as my example.

I simply was illustrating a real life example to Inspectordan , done perfectly to code, in the event he runs across such an animal. In your example he could see that if he saw #4 wire, 100 amp MCB, and a 200 panel, not to assume it was not to code, as his criteria would disallow my example.

Your example was done by a buffoon. (not referring to you), which I suppose certainly could happen by a DIY'er.

I am assuming all is done to code, everywhere, Silly me. I suppose now that I think of it, probably not so, is what your saying. But all things being equal,a PROPERLY installed service is rated by the MCB.

Correct?

Quote:

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Originally Posted by InspectorDan

You could NOT have a #4 wire feeding a 100 amp main. It would be unsafe and non-compliant since the conductor could not carry 100 amps of current without overheating.

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Actually Dan #4cu is the correct size for a 100A residential service.

Edit: Sorry Don, I didn't notice page 2.

Quote:

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Originally Posted by InspectorDan

You could NOT have a #4 wire feeding a 100 amp main. It would be unsafe and non-compliant since the conductor could not carry 100 amps of current without overheating.

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Are you positive about this?

Why does everyone think I just got my masters license yesterday? Never mind the one I let go from another state I had for years but don't plan to work in again, along with a State certified electrical inspectors license from that state. Keep in mind they just don't give these away to anyone.

How about this:

Quote:

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Originally Posted by donf

InspectorDan,
TK is correct. #4 AWG Copper is rated for 100 amps as a service feeder. I believe the code reference is T 310.15 (B) (6).

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Correct Don, thanks for filling in with this accurate detail.

Considering this is a residential topic we are discussing, this conversation is done. Don listed the only aspect I would have brought up.

And there are other technicalities regarding non-residential that is beyond the scope of this forum that I will not get into.

Dan, review Table 310.15 (B)(6) and get back to me with the other sizes of residential feeders that you may originally think are undersized.

So much for the declared humility.

Quote:

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Originally Posted by tkrussell

Why does everyone think I just got my masters license yesterday?

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TK, I hope you are not including me in this group. By this I mean I hope I didn't imply that you don't know what you are talking about. You obviously do.




Back on topic, I see no code prohibition in having a 200A main breaker on a 100A service entrance. Of course it is not a great installation being mismatched like that, but there is nothing illegal about it.

If you know of a code section pertaining to this I'll surely look it over. Thinking I missed something over the years I re-checked what I thought I knew and didn't come up with anything.

Stan,

Quote:

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Originally Posted by stanfortyman

TK, I hope you are not including me in this group.

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Absolutely not, certainly did not mean to refer to you at all. I know better. While you and I may disagree on certain aspects of things, but not code. We are in sync, brother.

Delete "everyone".

Just meant the newbies that only know small portions of the code.

Quote:

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Originally Posted by stanfortyman

Back on topic, I see no code prohibition in having a 200A main breaker on a 100A service entrance. Of course it is not a great installation being mismatched like that, but there is nothing illegal about it.

If you know of a code section pertaining to this I'll surely look it over. Thinking I missed something over the years I re-checked what I thought I knew and didn't come up with anything.

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Sorry, I read this portion too fast , thought it was to the OP at first, looks like your continuing with me.

If so,

With regards to residential, that is clear with table 310.15(B)(6), that is why I previously stated that conversation was done, Don found the right detail. There is no more leeway on residential feeders. Hopefully InspectorDan has been educated.

Residential is also stated in Sec 230.79 as a specific installation, which leads me to Sec 230.42 (A) 1:

To elaborate a bit on non-residential, service entrance conductors only need to be sized according the load as calculated per Art 220 as stated in Sec 230.42(A)1.

There are situations where the MCB could be larger than what appears to be correct. This is found with DESIGNED commercial and industrial applications.

I said I would not get into this in this forum, simply because it distracts from the residential question, and did not want to have to look up all this stuff at this time of day, but since you asked, here is where I will use our lingo:

Values I refer to below come from Sec 430,


An example, while an industrial plant may have a calculated load of 500 A 480 VAC 3P, and this is total RLA of course.

My SEC can be rated for 500 amps, for lighting, HVAC, misc loads, and here is the kicker... and a big motor.

The plant contains a large motor, say 200 HP 480 VAC with RLA of 240 A, and it has a LRA of 1450 A.

An inverse time CB can be 250% of RLA, 240 x 2.5 = 600 A.


My MCB can be 600 A, with 500 amp rated conductors feeding it.

The MCB along with the branch CB must be able to handle the LRA of the motor.

This is a fairly simplistic view, just trying to get my point across.

Dan, have you had a chance to review Table 310.15(B)(6) yet?

You can find it here: NFPA 70: National Electrical Code®

Takes a jumping through a few hoops to get to the actual code, but unless you have a code book with you, best method of reading the actual material.

And did you understand the subsequent detail I provided for non-residential installations?

Since you have inspector in your ID name, I am assuming that you're a home inspector. If that is true, I think it is critical that you understand the table Don directed you to,and my explanation.