Comment by a home inspector on my condo panel capacity

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ziggle

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Hi folks,

Most of my work is with low voltage stuff, so I need some help. I have a condo that is one of four units. Each unit has a 150 amp service. The four units are fed from a common 400 amp panel. The home inspector said this is a safety issue, but the city inspector said it is OK.

I don't see the safety problem. Each unit is limited to 150 amps, the rating of the the service panel breaker. They are all safe. The question is whether the 400 amp common panel is too low of capacity. It seems like it is possible we will get some breaker trips, but that there is no safety issue.

Comments?

Zig
 
article 220; calculate the loads, apply the demand reductions. The NEC is fairly conservative in most cases, the numbers should tell the tale, all else is needless speculation.
 
Think about this, If you add up the breaker sizes in one of those (4) 150A panels Im sure they would add up to way more than 150A. The size of your panels and service size is based on load calculations. Do a little research on this website, in the NEC in calculations, and let the HO, inspector know how this all works
 
ziggle said:
Hi folks,

Most of my work is with low voltage stuff, so I need some help. I have a condo that is one of four units. Each unit has a 150 amp service. The four units are fed from a common 400 amp panel. The home inspector said this is a safety issue, but the city inspector said it is OK.

I don't see the safety problem. Each unit is limited to 150 amps, the rating of the the service panel breaker. They are all safe. The question is whether the 400 amp common panel is too low of capacity. It seems like it is possible we will get some breaker trips, but that there is no safety issue.

Comments?

Zig
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Please tell the home inspector that he is not qualified to make a determination of this nature. It is perfectly within the guidelines of both the poco and the NEC and to concentrate more on termites and carpenter ants. Leave the electric issues to the pros.
 
Applicable Code Section

Applicable Code Section

It seems like NEC 220.84 Multifamily Dwelling (B) House Loads is applicable. I have no issue accepting that 150 amps is a reasonble panel size for each condo. The question is with the common panel. According to Table 220.84 Optional Calculations, the allowed demand factor is 45%. So it seems like the panel only needs to be 45% of the capacity of the 4 condo units. Am I thinking of this correctly?

Zig
 
No. You must perform a complete article 220 calculation for a multifamily dwelling to determine the service size. There are no shortcuts, there is no "ballpark", and you cannot size it based on the size of the sub-panels in each unit. Start at the beginning and end at the end. Anything else is just guessing and speculation. Since the Home Inspector is the one that has indicated that there is a problem, ask him to be so kind as to share his NEC Article 220 based Multifamily dwelling calculation figures with you. Be prepared for a blank stare...
 
I was thinking of inserting a comment, but haskindm said everything I would have said, and said it perfectly. I particularly like the "blank stare" comment. So I'll just say, "what he said."
 
haskindm said:
No. You must perform a complete article 220 calculation for a multifamily dwelling to determine the service size. There are no shortcuts, there is no "ballpark", and you cannot size it based on the size of the sub-panels in each unit. Start at the beginning and end at the end. Anything else is just guessing and speculation. Since the Home Inspector is the one that has indicated that there is a problem, ask him to be so kind as to share his NEC Article 220 based Multifamily dwelling calculation figures with you. Be prepared for a blank stare...
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That is the best way anyone could handle him.He very likely has no clue.Pass onto the person that hired him the answer he gives you.Or be nice and hand him a paper towel to remove the egg from his face.HI in itself is not bad idea but they need to know far more than most do.
 
Jim W in Tampa said:
That is the best way anyone could handle him.He very likely has no clue.Pass onto the person that hired him the answer he gives you.Or be nice and hand him a paper towel to remove the egg from his face.HI in itself is not bad idea but they need to know far more than most do.
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More importantly they need to realize that "a little knowledge is a dangerous thing" and that a 48-hour training class does not make an expert. Most HI's that I have dealt with have been pretty good, but there are some people that think they know everything when in reality they know very little.
 
ziggle said:
Hi folks,

Most of my work is with low voltage stuff, so I need some help. I have a condo that is one of four units. Each unit has a 150 amp service. The four units are fed from a common 400 amp panel. The home inspector said this is a safety issue, but the city inspector said it is OK.

I don't see the safety problem. Each unit is limited to 150 amps, the rating of the the service panel breaker. They are all safe. The question is whether the 400 amp common panel is too low of capacity. It seems like it is possible we will get some breaker trips, but that there is no safety issue.

Comments?

Zig
Click to expand...
I think you should ask the HI what NEC article is being violated, or what exactly the safety issue is.

Even if more current is drawn through the individual 150A sub-panels than the 400A sub-panel can supply, the only bad thing that will happen is the main on the 400A panel will trip. A nuisance but not a safety issue.

It seems unlikely that four typical condos could use that much juice anyway.
 
haskindm said:
ask him to be so kind as to share his NEC Article 220 based Multifamily dwelling calculation figures with you. Be prepared for a blank stare...
Click to expand...


I'm sure that the HI did a load calculation.:rolleyes:
 
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