Service conductors in parallel

[11Haze29]

Industrial application to install 2500KVA padmount xfrm,480V, 3ph. Under normal condition I would feed 3200amp switchgear with 5 each 800a branch breakers. But customer wants cheap as possible, so I want to ask what you think of this. Article 230.71 permits six switches/breakers for a service. Is it possible to set up five each, 800A fused disconnects in the electric room, then take two each 500MCM copper XHHW feeders from the line side of each FSD back to the transformer lugs. FSD's will be rated for 'Service Entrance'. The FSD lugs would be rated 75C, Size 500MCM in 310.16(75C) is rated 380amps. 240.4(B) permits devices 800A or less to round up the conductor ampacity. So if 500MCM can round up to 400A, in parallel can it be 800Amps.

Will most utilities permit you do this. When I see the six breakers its usually from a main bus. But I can't see why it can't also be done as described above.

Welcome your suggestions.

 

[augie47]

If POCO has no problem, it is Code compliant. AHJ may ask for load calculations since you have 760 ampacity with an 800 amp fuse.

 

[jim dungar]

If this is a customer owned transformer, these conductors will need to be protected under the tap rules of 240.21(C). You will probably have problems with a maximum conductor length of 10' which rules out 240.21(C)2. You are planning on using multiple sets of 'small' conductors so 240.21(C)1 and 3 are not applicable. This leaves 240.21(C)6 as the governing section. So, what is the transformer voltage ratio and the primary protective device?

Although, because this is a supervised industrial application, you may try for relief under 240.92(C), but 240.92(C)(1) may cause problems.

 

[iwire]

If this is a customer owned transformer

If this is a customer owned transformer this thread is misnamed.

 

[jim dungar]

If this is a customer owned transformer this thread is misnamed.

Technically, you are correct. :roll:

And, the OP is referencing section 230.71 (and I hope 230.90(A) exception #2 and 3).
But, practically, I know many people that refer to all transformer secondaries as services. This is why I specifically clarified my comment.

 

[11Haze29]

Sorry I didn't make that clear - this is a utility owned transformer, and the cables from the secondary transformer lugs to the FSD's are the lateral service conductors. Consequently there is no 10ft rule before the secondary overload rule, and the FSD's are the overload and service disconnect, to which you are allowed six total per code. I've just never done it before with this size FSD's.

I don't generally consider 'all' secondaries as a service. I consider a service as the primary electric supply from the outside world into the building. So if I had a owner owned pad mount and I had to run 100ft to the building to get into a switchboard, I consider that a service and not subject to the secondary 10ft rule for an overload. But that's about where it ends for me.

 

[don_resqcapt19]

... So if I had a owner owned pad mount and I had to run 100ft to the building to get into a switchboard, I consider that a service and not subject to the secondary 10ft rule for an overload. But that's about where it ends for me.

Those conductors would not be service conductors. The transformer secondary conductors would be feeders and subject to the rules in 240.21(C). For this application 240.21(C)(4) may apply giving you unlimited outside length.

 

[kingpb]

With what you are describing, first, you need to make sure the equipment you are considering using can be purchased as "service entrance rated". I bring this up because I ran into this before, where the equipment was certainly capable of the necessary ratings, but it could not be gotten with the all important label, without a third party testing agency to come and certify it. That in itself may drive the cost over your normal install.

Second, is what your proposing, really cheaper when you look at installed cost, and how much are you really saving? It seems odd that an Owner that needs a 2500A service, is trying to scrimp in the area that will keep his whole operation going. Better, make sure your Lien papers are in orders.

Lastly, better check with the POCO service engineer, they may not be keen on the idea, and if they say no, then it really doesn't matter. POCO has standard methods for services and they won't accept just anything, regardless of what the AHJ says.

 

[masterinbama]

I would also run 1 set of spare conduits in case you need to set your 6th service disconnecting means in the future.

 

[11Haze29]

I disagree that these are feeders, they are the service conductors. I plan to check with the utility first and see what they say also.

This is a Waste Transfer Facility and the owner is cheap, and the place is filthy. So in a way, having FSD's is simple, easy to change fuses, requires no breaker testing, and is a bit more fool proof than having switchgear that sits for 30 years and is never serviced.

 

[kingpb]

I plan to check with the utility first and see what they say also.

Good idea.........

So in a way, having FSD's is simple, easy to change fuses, requires no breaker testing, and is a bit more fool proof than having switchgear that sits for 30 years and is never serviced.

Yeh, but that also means some unqualified person is going to be putting in a new fuse, with line terminals energized, and wait til you see what they put in place of the fuse after a fuse blows........I think a piece of aluminum from a scrap lawn chair leg might just do nicely.:grin:

 

[don_resqcapt19]

I disagree that these are feeders, they are the service conductors. I plan to check with the utility first and see what they say also. ...

Where is the service point?
If the transformer is utility owned, the secondary conductors are most likely service conductors. If the transformer is customer owned, the secondary conductors are most likely feeders.

 

[tish53]

One other issue to consider.

While it may be a little cheaper to install 6 "mains" in the form of fuse disc. switches, the practical matter of repair, maintenance, etc. will be greatly complicated. The Utility will need to be called to disconnect power to the entire operation, just to safely work on one of the 6 feeds. In our world that "inconvience" is worth much more then the small amount saved up front.

 

[LarryFine]

Tish, welcome to the forum!

Where in Richmond are you, and what kind of work do you do most?

 

[jim dungar]

So if I had a owner owned pad mount and I had to run 100ft to the building to get into a switchboard, I consider that a service ....

I thought this might be the case, which is why I clarified my comment.

I have seen some installations like this where the utility rules govern the conductors, and other where the NEC applies.

Just curious, although it is sometimes important, where is your metering point?

 

[david luchini]

The description of running of separate sets (of two sets of 500mcm each) from each FSD in the electric room to the transformer terminals got me thinking. The "service lateral" is defined as the the conductors between transformers...and the first point of connection to the service entrance conductors in a terminal box, meter or other enclosure either inside or outside the building. Where there is no terminal box, etc, the point of connection is considered to be the point of entrance of the service conductors into the building. It sounds like the conductors from each FSD to the transformer terminals would be "service conductors" inside the building and "service laterals" outside the building.

Five separate service laterals would indicate five separate services, which would violate 230.2: Number of Services. I know there is a "capacity requirement" where service are in excess of 2000A are permitted to use additional services, but I don't interpret this as allowing a 2200A service to be split into (11) 200A services.

Interestingly, 230.40 Ex. No. 2, would allow five sets of service-entrance from one service lateral to each of the five separate service disconnect switches. But there still must be only one service lateral. So to run the five sets as proposed, there must first be one service lateral from the transformer to a terminal box, and then five sets of service-entrance conductors from the terminal box to each service disconnect.

Am I misinterpreting the number of services section?

 

[Npstewart]

I wish I could remember the section to refer to, but one time I got a rejection for feeding a 400A panel from a step down transformer with #500s. Im trying to remember the section but when you are coming from a transformer, or feeding with parrel conductors, you can't round up. You can still use 500s if feeding say a 400A subpanel from another panel. Ill see if I can post the section here in a little.

 

[david luchini]

I wish I could remember the section to refer to, but one time I got a rejection for feeding a 400A panel from a step down transformer with #500s. Im trying to remember the section but when you are coming from a transformer, or feeding with parrel conductors, you can't round up. You can still use 500s if feeding say a 400A subpanel from another panel. Ill see if I can post the section here in a little.

I think you're referring to section 240.21(C) (overcurrent protection for transformer secondary conductors.) It says the ampacity of the secondary conductors shall NOT BE LESS THAN the rating of the ocpd at the termination of the secondary conductors. 500mcm with an ampacity of 380 is less than the 400 ocpd, therefore, not allowed.

However, that section wouldn't apply to the original post, which relates to service conductors.

 

[jim dungar]

Interestingly, 230.40 Ex. No. 2, would allow five sets of service-entrance from one service lateral to each of the five separate service disconnect switches. But there still must be only one service lateral.

It is possible that the transformer secondary spades/terminals can be considered the service lateral.

 

[benaround]

I'm thinking some good distance between the transformer and these 800a FDS might be a

good idea.