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200 amp or 400 amp service?


kimball gray
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That's a great question. I've often wondered myself what the true answer is. Typically, the cable coming into the the meter base isn't visible. I always call out 2 x 200 as 400 AMPs of service and 2x150 as 300 AMPs of service. But, often even overhead main service entry cables will be smaller than they're supposed to be, and the power company justifies it because the cable is "air cooled".

So, the way I understand it, the service cable doesn't necessarily have to be rated for 400 AMPs, but within a percentage of it. Therein lies the real question...

I'd be interested to learn how others call this out, as well as what the true technical answer is.

I'm sure Douglas or some other electric savvy fellow with chip in soon.

Well, I took so long in writing the post that Kevin may have offered an answer. I'd sure like to see this one nailed down.

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With multiple panels in parallel, the capacity of the service is determined by the size of the service conductors. If a load calculation on a particular dwelling yields a required ampacity of 320, then twin 200 amp panels might be selected for the simple reason that no one makes a 320 amp panel or a 160 amp panel. Sometimes multiple panels are used to obtain more breaker slots than a single panel could furnish.

Marc

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If it's a class 320 meter, it'll nearly always be a 400 amp service. The power company only needs the meter to be rated at 80%.

- Jim Katen, Oregon

This always has been the source of a bit of confusion in my own mind.

So then, what we're really describing, regarding "service" in our reports, is NOT the rating of the main service cable, but rather the total potential usage. The cable used for delivery is at the discretion of the local poser company. Si?

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This always has been the source of a bit of confusion in my own mind.

So then, what we're really describing, regarding "service" in our reports, is NOT the rating of the main service cable, but rather the total potential usage. The cable used for delivery is at the discretion of the local poser company. Si?

I am not sure whether you are asking about the service entrance cables or the wiring installed by the power company.

The NEC tables are used to properly size the service entrance conductors. The conductors under control of the power company are sized based on a different set of rules and result in being several sizes smaller than the SECs.

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This always has been the source of a bit of confusion in my own mind.

So then, what we're really describing, regarding "service" in our reports, is NOT the rating of the main service cable, but rather the total potential usage. The cable used for delivery is at the discretion of the local poser company. Si?

I'm not sure I understand your question. What Kurt suggested, regarding twin 200 amp panels, might cause some clients to believe that they had 400 amps of service capacity which may not be the truth.

Keep in mind:

1) A single panel that lacks a main breaker is permitted as long as the '6 disconnect' rule is not exceeded. This also applies to installations with multiple panels without a main disconnect, even when each panel has it's own 'main' disconnect. Turning one individual 'main' off on one panel does not remove power from the other panels, so, technically, there is no longer a main breaker and the '6 disconect' rule must be observed (6 panels maximum, provided that each panel has it's own 'main' breaker).

2) If there is only one panel installed and it has a main breaker, that breaker specifies the ampacity of the service to that dwelling.

3) If power is furnished to a dwelling by either; a single panel without a main breaker; by multiple panels without a single main disconnect that removes power from the entire dwelling, then the ampacity of the service is determined by the rating of the main service conductors. The rating of the individual tap conductors feeding each individual panel in a multi-panel installation does not determine the ampacity of the service.

Marc

EDIT: spelling

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2) If there is only one panel installed and it has a main breaker, that breaker specifies the ampacity of the service to that dwelling.

Not necessarily true, is it?

I've seen cases where contractors come in to upgrade an old 60 Amp service and the only thing they did was install a 200 Amp panel.

The original SEC and meter base were still there along with the original power coming wiring to the meter base.

-

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2) If there is only one panel installed and it has a main breaker, that breaker specifies the ampacity of the service to that dwelling.

Not necessarily true, is it?

I've seen cases where contractors come in to upgrade an old 60 Amp service and the only thing they did was install a 200 Amp panel.

The original SEC and meter base were still there along with the original power coming wiring to the meter base.

-

I've seen that a few times, myself. Maybe it only happens in ass backwards Kentucky.

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2) If there is only one panel installed and it has a main breaker, that breaker specifies the ampacity of the service to that dwelling.

Not necessarily true, is it?

I've seen cases where contractors come in to upgrade an old 60 Amp service and the only thing they did was install a 200 Amp panel.

The original SEC and meter base were still there along with the original power coming wiring to the meter base.

-

I've seen that a few times, myself. Maybe it only happens in ass backwards Kentucky.

Me three (although I don't think it was as drastic as 60 - 200). And, when the purchasers alert the local power company, the typical response is that, since it was overhead and air cooled, there was no threat of overheating.

Now and then, they change it out, but not usually, unless the gap is pretty large.

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2) If there is only one panel installed and it has a main breaker, that breaker specifies the ampacity of the service to that dwelling.

Not necessarily true, is it?

I've seen cases where contractors come in to upgrade an old 60 Amp service and the only thing they did was install a 200 Amp panel.

The original SEC and meter base were still there along with the original power coming wiring to the meter base.

-

I've seen that a few times, myself. Maybe it only happens in ass backwards Kentucky.

It happens here too. It's a serious mistake to do that. 200 amps passing through a conductor rated at 60 amps will generate more than 11 times as much heat in the conductor, and the main breaker won't trip to protect it. It's an Rx for a fire. Many electrical fires in dwelling are sourced at the electrical service entrance, at least that what I hear (read).

Marc

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2) If there is only one panel installed and it has a main breaker, that breaker specifies the ampacity of the service to that dwelling.

Not necessarily true, is it?

I've seen cases where contractors come in to upgrade an old 60 Amp service and the only thing they did was install a 200 Amp panel.

The original SEC and meter base were still there along with the original power coming wiring to the meter base.

-

Erby and John, I think you know this is a bad thing, but your sarcasm could be misinterpreted here. Marc is correct. A 200 amp breaker will allow for a load up to 200 amps before power is disconnected by the breaker. If the service conductors are undersized, such as what you'all Kentuckians are describing, they will simply overheat as the loads increase. Bad.

Someone correct me if this is wrong. Two 200 amp panels may be supplied by a meter rated only for 320 amps. because there is an 80% rule. I think the idea is that the continuous load will never exceed a total of 320 amps, although there is a capacity for 400 amps. or something like that.

In my country, we do not have a 6 breaker rule. We will always see a main breaker, so that part of inspecting is made easy. If I see a service panel, not a subpanel, with no main breaker, it is from the 50's and needs to be replaced.

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Someone correct me if this is wrong. Two 200 amp panels may be supplied by a meter rated only for 320 amps. because there is an 80% rule. I think the idea is that the continuous load will never exceed a total of 320 amps, although there is a capacity for 400 amps. or something like that.

You can put up to six of them, any size, though I really can't imagine a real life situation where so many branch circuits would be required for a service rated at only 400 amps. I've seen six 200 amp disconnects in a commercial installation where the service was 800 amps but four of the disconnects were feeding AC/Heat package units.

Marc

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So, getting back to a point, is calling it 2-200 amp services appropriate? That's what the cables into each panel say.

I'm really not going to suggest to anyone they have a 320 amp service.

Inappropriate, unless you check the size of the service conductors against that table in the codes that reveals what it's rating is.

I don't bother with even doing that. I just mention that two 200 amp panels are installed and that I do not know the ampere rating of the electrical service entrance.

Marc

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. . . Someone correct me if this is wrong. Two 200 amp panels may be supplied by a meter rated only for 320 amps. because there is an 80% rule. I think the idea is that the continuous load will never exceed a total of 320 amps, although there is a capacity for 400 amps. or something like that.

Sort of. The meter doesn't limit the amount of current that can pass through the system but it still has to be properly sized for the system or it will read inaccurately; if it's severely overloaded, it could even be damaged. For most modern installations, a 400-amp residential service will have a class 320 meter, which is rated for a continuous load of 320 amps and which can perform at 400 amps for short periods of time with no risk of damage. A house will, for all practical purposes, never use anywhere near this much power on a continuous basis though. In fact, this meter is calibrated to 5 amps at the low end and 50-amps at the high end.

- Jim Katen, Oregon

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So, getting back to a point, is calling it 2-200 amp services appropriate? That's what the cables into each panel say.

I'm really not going to suggest to anyone they have a 320 amp service.

It's inappropriate to call it two services. It's only one service.

If there's a class 320 meter and 2, 200-amp panels, it's almost certainly a 400-amp service.

I'm not aware of such a thing as a 320-amp service.

- Jim Katen, Oregon

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Inappropriate yes, I've never liked calling it that. But, it's 2-200 amp panels fed with separate 200 amp cables, each with it's own 200 amp disconnnect.

And it's not a 400 amp cable feeding the meter can.

So, I call it the wrong thing because I can't think of how else to describe it satisfactorily.

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Inappropriate yes, I've never liked calling it that. But, it's 2-200 amp panels fed with separate 200 amp cables, each with it's own 200 amp disconnnect.

And it's not a 400 amp cable feeding the meter can.

So, I call it the wrong thing because I can't think of how else to describe it satisfactorily.

"The configuration of the electrical service entrance is 120/240 volts, single phase with two panel boards installed in separate, adjacent enclosures. There was no main breaker or fusible disconnect installed, so I was not able to determine the ampere size of the service."

I don't see a need to mention the ampere size of each panel since that info no longer reveals the ampere specification of the overall service. It's similiar to a situation where a single panel is installed and that panel does not have a main breaker. I don't know the size of the service. If you mention the ampere rating of the panel, you may mislead the client.

Marc

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I geek out on this stuff, too. But don't forget that maybe one out of a hundred customers will care and/or take time to read what you've written RE the electrical service, much less understand what it means. Like so many other things, they just want to know whether it's okay or not.

The Standards require a description of the heating system(s), as well, but how many of your customers can tell you what the BTU rating of the "heater" is a week after the inspection?

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Yeah, we are required by the State to "describe" what's there; I'm not going to say I can't tell.

And, this goes to what Bain just said......folks aren't going to understand or care about fine tuned distinctions.

It's a couple 200 amp rated panels with separate disconnects, each fed with separate 200 amp cables.

What should I call it?

It kind of gets to the same idea of "is it 110 or 120v?"........does it matter to anyone other than us and a bunch of double e's?

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