325 amp service

[docluv]

I have a feeder coming in from the vault to the house. It is 325amps. Goes up to the meter socket. This is where I get a little confused. I asked a superior at work this what he said. we will go in a gutter,then nuckle splice in to two sepreat 200 amp disconects.then 4/0 to the two seprate 200amp 40 space panels. How is this legal? Are both feeders to the disconects going to carry 325?If the disconects are rated at 200amps would the lugs and the bus bars eventualy heat up and go caput? It just raises alot of potential questions,and possable problems in the future I think.But I can't wire houses on what if's. Any info on this type of set up would greatly help and be appreciated. thanks doc.

 

[Dennis Alwon]

In our area the power company is responsible for the power to the meter base and it is often much smaller than the service size would allow under the NEC. But the power company is responsible for it and if there are problems, it is there troubles, not ours. You can only get meter bases rated 325 amp, otherwise you have to have a CT cabinet. I am not sure why but our area will let us hook up a 400 amp service ( 2- 200 amp Main Breaker panels) to this meter. The power company does not want a CT cabinet unless it is higher than a 400 amp service. We never have any problems-- go figure.

 

[George Stolz]

Doc, welcome to the forum.

we will go in a gutter,then nuckle splice in to two sepreat 200 amp disconects.then 4/0 to the two seprate 200amp 40 space panels. How is this legal?

We're given the overcurrent protection requirements for services in 230.90(A). That states that the OCPD cannot exceed the ampacity of the conductor.

However, exception (3) to that section permits a pair of breakers to provide the protection if the load calc is less than the ampacity of the conductors.

From what I've heard, what you've described is a common method for providing a 400A service to a residence.

Are both feeders to the disconects going to carry 325?

Not if the service conductors going into each 200A disconnect are protected at 200A.

 

[George Stolz]

Does this picture look like the setup in question?

(Aside from the gutter and splices - in my picture, I spaced that and made the meter-socket have double-barrel lugs on the load side for simplicity.)

 

[suemarkp]

If your service lateral isn't rated for 400A, you may want to consider a 125A panel and a 200A panel. But if the load calculated to 325A, it will be nearly impossible to get that from a dual panel setup since you lose some headroom when you calculate the load on just one panel instead of the entire service, or a single large load could put you just over a given panel's limit. I have a 320/400A meter with 400A service conductors and the load calculated to 340 amps. I had a hard time putting things in the proper place without overloading a given panel, and I have two 200A panels.

You can have the sum of the main disconnects be larger than 325 amps, as long as the wire ampacities and load calculation match. But a residence tends to get things added without people doing future load calculations, so its best to idiot proof them.

 

[infinity]

Where in this scenario is the OCPD for each panel?

 

[allenwayne]

Where in this scenario is the OCPD for each panel?

The OP said there would be 2 200 amp disconnects that feed 2 200 amp panels.I`ve done countless 320/400 services as in Georges illustration and have never used a trough.There would be nothing wrong with it other than wasting time and material.

 

[infinity]

The OP said there would be 2 200 amp disconnects that feed 2 200 amp panels.I`ve done countless 320/400 services as in Georges illustration and have never used a trough.There would be nothing wrong with it other than wasting time and material.

Did the OP say that they are fused disconnects?

 

[George Stolz]

In a private conversation with the OP, I established that the service conductors up to the line side of the meter are provided by the utility, so are not in question. The conductors he was concerned about are from the line side of the meter, to the gutter, before they split off to 4/0 AL to each 200A disconnect.

I guess the meter socket and the conductors on the load side of the meter to the gutter were to be rated for 325A.

In the conversation, I recommended upsizing the conductors to 400A, but I forgot about the meter socket itself.

I don't recall overcurrent protection coming up, but he might have mentioned that both disconnects contained OCPD. Perhaps the original poster will get back to us, now that I've effectively forgot the details.

 

[allenwayne]

Did the OP say that they are fused disconnects?

No he didn`t since the disconnects I use are 200 amp MBR disconnects,why even bother with a non fused disconnect in a sitation like this.I ASS U ME D

 

[docluv]

sorry I wasn"t realy descriptive enough.

sorry I wasn"t realy descriptive enough.

I guess I have alot of questions that stem from this service. It isn't like I havent done a butt load of services,It's more like I don't realy understand what or why my company has asked me to do it this way.I see a possibility of potential problems. George's picture is astetically corect. and as he said I am confused about how the wire between the meter and the disconects are protected? Is it realy just the two 200amp disconects? why wouldn't the disconects burn up? The lugs and bus bars are rated at 200amps not 325? Am I too understand that by putting nuckle splices on the wire lowers the amps?Why is it that when I split a 15amp branch circuit with a wire nut and pigtails, my pigtails both read 15amps? It's the same idea, just bigger matterial at the panel. So I realy am most questionable if this would even pass an inspection.I don't get to get here often but I will try to check in a lot closer for your coments.thanx for all your help understanding. Just another dumb sparkie tryin'to learn somtin. (not that I get a bonus or raise for doing it righ the first time!) DOC LUV!@#$%^&*(

 

[George Stolz]

I am confused about how the wire between the meter and the disconects are protected? Is it realy just the two 200amp disconects? why wouldn't the disconects burn up?

If they have overcurrent protection in them, why would they? When they exceed 200A they shut off, either by breaker or by fuse. These are fused disconnects, aren't they?

Am I too understand that by putting nuckle splices on the wire lowers the amps?

No, the current (amps) is determined by the load.

Why is it that when I split a 15amp branch circuit with a wire nut and pigtails, my pigtails both read 15amps?

If that's so, you've clamped to a point on the circuit before the two wires split to their different loads. Check out this diagram:

From this panel is a four-wire cable: 3 hots, 1 neutral.
At the panel, with an amp-clamp, the Black load is 7A, Red load is 7A, Blue load is 7A. Each fluorescent light draws one amp. Between Black #7 and Black #6, those conductors are experiencing one amp of current. Between #6 and #5, those conductors are seeing two amps, and so forth.

If you slap an amp-clamp between on the black between #5 and #4, the amp clamp will read 3A.

So, by comparison, if you have two panels with loads, the conductors feeding each panel are only carrying the amps that are depending on those conductors to work. Essentially, the home run in the diagram is the same as the 400A conductors in your service: If, after they branch off, the branches are protected at 200A and the trunk is worth 400A, the branches can't damage the trunk.

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I think another key to understand is a fundamental that Bob touched on in a recent thread.

A 400A meter socket is good for a continuous load of 320A.
A 400A breaker is good for a continuous load of 320A.

This "325A meter socket" is not manufactured, to my knowledge. What you probably have is a 400A (320 continuous) meter socket. Which means, so far, you have a 400A service.

A service is a service - if you think about it, all service conductors are protected on their load side, unlike everything else that we protect on the line side. We have no way to protect service conductors on the line side, they're inaccessible to us (and the NEC).

So, we protect them in a less complete fashion, on their load side. Since service conductors are essentially unprotected, this is why we are required to keep them almost entirely outside. All service conductors are unsafe.

If you install 400A conductors, and then downsize into two 200A panels, then you will have basically two 200A services.

Functionally, when each panel is drawing 200A, then every point along the service conductors are protected to their ampacity. If panel A pulls 230, and so does panel B, then we have 460A total; but each breaker on each panel will trip, so the big conductors will not see any more current than the smaller ones, proportionally. All conductors can withstand some overloading prior to their OCPD tripping.