320amp vs 400amp

[Fitzdrew516]

You need to calculate load before you know what minimum size service disconnecting means is necessary.

When sizing conductors and overcurrent devices for an individual load it is simpler - that load is either continuous and 125% rule applies or it is not continuous - if using a standard overcurrent device. If using a 100% rated device there is no 125% to deal with.

Multiple loads of same type is sometimes a little more complex but somewhat similar - maybe a feeder that only supplies motors fits this category.

If you are using art 220 for calculating multiple loads then you have already factored in where needed 125% for continuous loads, and in some cases reduced the load because of allowable demand factors. If your result is 375 amps then you need a 375 amp minimum conductor and 375 amp minimum overcurrent device. You likely go next standard size higher which is 400 amps with overcurrent and the conductor will depend on ampacity adjustments that may be required on top of base ampacity.

Yes. I'm saying if your combined calculated load could be over 400A because a "100% rated breaker" is really just a breaker rated for 100% of continuous loads and therefore you could argue the opposite is true and that it is rated for 125% of non-continuous load.

Let's use the example Jumper posted earlier -

200A non continuous load plus 160A continuous load would be a calculated load of 400 amps. So this would be sufficient for a regular old "80% rated breaker" (btw I hate calling them that bc it is what adds to people's confusion).
However, if you were to use a 100% rated breaker then since it is rated for 100% continuous use isn't that the same as it being rated for 125% of non-continuous use? Then I could technically add 100A more (non-continuous) load onto this service. Then we would size the wire to the calculated load which would be 300A non-continuous load + 160A continuous load = 500A.

 

[iwire]

Y therefore you could argue the opposite is true and that it is rated for 125% of connected load.

A nit pick here but not 125% of the connected load 125% of the NEC calculated load.

 

[jumper]

Yes. I'm saying if your combined calculated load could be over 400A because a "100% rated breaker" is really just a breaker rated for 100% of continuous loads and therefore you could argue the opposite is true and that it is rated for 125% of connected load.

Let's use the example Jumper posted earlier -

200A non continuous load plus 160A continuous load would be a calculated load of 400 amps. So this would be sufficient for a regular old "80% rated breaker" (btw I hate calling them that bc it is what adds to people's confusion).
However, if you were to use a 100% rated breaker then since it is rated for 100% continuous use isn't that the same as it being rated for 125% of non-continuous use? Then I could technically add 100A more (non-continuous) load onto this service. Then we would size the wire to the calculated load which would be 300A non-continuous load + 160A continuous load = 500A.

Fitz, you are really just complicating this with your 100% rated breaker IMO. The use of one is rare and throwing it into this scenario is creating confusion.

I have never installed one and I would surmise most average guys have not either.

 

[Fitzdrew516]

A nit pick here but not 125% of the connected load 125% of the NEC calculated load.

A necessary nit pic at that! I misspoke (typed). I have edited it to say "non-continuous" load.

 

[Fitzdrew516]

Fitz, you are really just complicating this with your 100% rated breaker IMO. The use of one is rare and throwing it into this scenario is creating confusion.

I have never installed one and I would surmise most average guys have not either.

Yeah - Sorry for hijacking the thread, but I'm just thinking out loud here. What if this was an existing service and you're trying to add load to it, but it has a standard 400A breaker in it? As long as the service equipment will accept a 100% breaker this could be an easier option than upgrading the service gear.

I had a situation a few years ago that fell into this category. That's why I'm throwing it out there lol.

 

[jumper]

Just for clarity I will post the rules for using a 100% rated assembly:

Where the assembly, including the overcurrent
devices protecting the branch circuit(s), is listed for opera-
tion at 100 percent of its rating, the ampere rating of the
overcurrent device shall be permitted to be not less than the
sum of the continuous load plus the noncontinuous load.

 

[jumper]

Yeah - Sorry for hijacking the thread, but I'm just thinking out loud here. What if this was an existing service and you're trying to add load to it, but it has a standard 400A breaker in it? As long as the service equipment will accept a 100% breaker this could be an easier option than upgrading the service gear.

I had a situation a few years ago that fell into this category. That's why I'm throwing it out there lol.

Not so simple as adding a breaker. See the rules I just posted. The whole kit and kaboodle is gotta be rated for 100%.

 

[iwire]

Fitz, you are really just complicating this with your 100% rated breaker IMO. The use of one is rare and throwing it into this scenario is creating confusion.

I have never installed one and I would surmise most average guys have not either.

I agree on added confusion.

As far as the use of 100% breakers I only know of one service we built with a 100% rated main breaker. The utility would not provide a service over 800 amps from a pole mount transformer but the customer has many continuous loads so our engineer chose the 100% rated breaker.

So basically it was used because there was little other choice unless the customer would not give up the space for a pad mount. It was in the city so space for parking was more important than space for a pad mount.

An interesting side note, the customer burned up two pole mount transformers before the power company decided to use a larger one.

 

[Fitzdrew516]

Not so simple as adding a breaker. See the rules I just posted. The whole kit and kaboodle is gotta be rated for 100%.

I agree with you. What I'm saying is it's easier to replace a breaker and wire than the gear itself plus the wire. This is assuming that the gear is rated to accept 100% breakers as some (possibly most) gear is not. Anyway - this is completely off topic as you said. So let us digress to the original topic at hand.

 

[mwm1752]

NO!

If your properly done NEC load calculation results in 400 amps you may use a class 320 meter. It is rated up to 400 amps.

If the meter base not the meter is rated at 320 amps you cannot put a 400 amp load on it -- but since your specs rate the meter base at 400 amps you may put a 375 amp load on it :thumbsup: -- my statement on rating of equipment to load still stands

 

[iwire]

If the meter base not the meter is rated at 320 amps you cannot put a 400 amp load on it -- I do not know about the specs of your 320 class c meter

I have posted a link twice in this thread showing class 320 meter sockets are rated 400 amps max.

 

[meternerd]

I am going to point out that a 320 meter is not '320 amps' it is a class 320 meter.

http://www.cooperindustries.com/con...ing_equipment/ring-type_metering/Class320.pdf

Just to add to the confusion....a 200A service gets a Form 2S Class 200 meter. So, shouldn't a 400A service get a Form 2S Class 400 meter? Back in the day, a self-contained (no CT's) meter installation for a 400A service used a bolt in Form 2K meter, which was rated 400A. K means K-base, which is bolt in. Later on, they developed a Form 2S (S means socket base) for the 400A service. Why they called it a Class 320 is still kind of a mystery because there's no such thing as a Class 160 meter. It is still designed to meter a 400A service. There are still a lot of older K base installations, but I'm betting most have had a socket base adapter installed so they can use a Class 320 meter. Much easier to exchange a socket base than a bolt in. Here's another twist....CT meters are rated Class 20, meaning a current rating of 20A so you can use a CT that is rated TRF (Thermal Rating Factor 4.0) That means the CT can handle 4 times its nameplate rating. Thus a 200:5 CT (200A primary, 5A secondary) can meter up to an 800A service, which would produce a 20A secondary current. Saves a bunch on inventory if you can use the same CT for 200A to 800A. Plus, the lower ratio means more secondary current, which means better light load resolution. If you used an 800:5 CT, at 200A it would only put out 1.25 A. At lower load it would even be worse. Add a little secondary CT burden and you get under registration. Not good. Fun stuff for sure!

 

[mwm1752]

I have posted a link twice in this thread showing class 320 meter sockets are rated 400 amps max.

Did you see my edit???

 

[mwm1752]

Look what I found -- a siemens ITE 400 amp meter/main rated at 320 amp continuous load

 

[iwire]

Look what I found -- a siemens ITE 400 amp meter/main rated at 320 amp continuous load

Right, and it's good for a 400 amp NEC calculated load.

 

[iwire]

Did you see my edit???

If I had it would have been in my quote.

 

[mwm1752]

Right, and it's good for a 400 amp NEC calculated load.

so its ok to have 400 amp load on 320 amp max rated buss?

 

[Carultch]

so its ok to have 400 amp load on 320 amp max rated buss?

I don't think anyone is saying that. What the consensus is, is that it is ok to have a 400A non-continuous load in a class 320 metering assembly.

 

[iwire]

so its ok to have 400 amp load on 320 amp max rated equipment?

:slaphead: NO!

But lets look at what you said (I can't read the small printing on your link, too small But I can see it has a 400 amp main breaker)

Look what I found -- a siemens ITE 400 amp meter/main rated at 320 amp continuous load

It is rated 320 amps continuous and 400 amps non-continuous or as the link says 400 amp max.


Pick a standard 400 amp breaker of the shelf, it is rated 320 amps continuous and 400 amps non-continuous.

 

[mwm1752]

I posted a meter/main that has a continuous 320 amp rating for the equipment -- - All service calulations are a continuous load and non continuous load -- If you service calulation is greater that the eqiupments rating that is non compliant -- I was just told that the maximum 320 amp rated meter/main is compliant to be used in a 400 amp service calulation -- the equipment link showing the class 320 amp metering assembly calls out the maximum contiuous load as 400 amps not 320 amps.