Upsizing Existing Commercial Electrical Service

[north star]

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I have an existing manufacturing / processing facility

that is upsizing their existing electrical service to a

400 amp. [ 480 volt ] size......The main distribution

panel will be a 400 amp. service, with some

sub-panels downstream......Also, an outdoor, pad

mounted transformer for the various motors onsite.

What issues do I need to be looking for? ...size &

number of the gec's, ...size & type of grounding

electrodes, ...clearances, ...proper labeling of

panels and panel directories, other?

Thanks for your input!

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[Dennis]

The gec is based on the size of the service conductors. Look at table 250.66 esp. the notes to the table. Depending on the install it may be as small as #2 but may require 1/0 or larger if their conductors are larger than required. They obviously would need 2 rods unless they have a concrete encased electrode or other type like a ground ring, etc.

The building steel must be bonded with the same size as required for the gec whether the steel is an electrode or not. Of course the metallic water pipe must be bonded also.

When we do a 400 amp service we may have 2- 200 amp panels with 3/0 copper feeding each panel. In that case a #2 copper GEC works. If there are parallel runs to one 400 amp enclosure then you must add the size of the conductors together and then match them to T. 250.66.

We can help with that if you know what size conductors and how many. Specifically you will be using Chapter 9 Table 8 cir. mil column to determine the parallel runs.

 

[Dennis]

All transformer secondaries must be connected to the Grounding electrode also. Each service disconnect shall be permanently marked to identify it as a service disconnect. 230.70(B)

 

[north star]

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Thanks Dennis for your reply!

I have one main, 400 amp. distribution panel with a ct meter

installed in it.......Downstream of this ct cabinet, is (1) 400 amp.

panelboard with a fused switch, ...(2) 400 amp. panelboards

w/ocpd's in each panel........(1) 45 kva pad mounted

transformer, 480 primary, 208/120 secondary, w/ (1)

200 amp. fused switch panelboard, and (1) 225 amp.

panelboard with 42 ocpd's & one 125 amp. sized breaker

in it.............No gec's, ...grounding electrodes, ...size

of conductors [ of any type ], ...disconnect locations,

...underground conduit type or size, and on, and on,

and on, and on.

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[Dennis]

Well if the panelboard can handle 400 amp breakers on the buss- I am surprised that it can- that in itself would not necessarily be a violation. The load is critical. I would ask for a service calculation.

Not sure about commercial boards but residential boards are usually limited to so many amps per finger. Commercial panels are often bolt on so I am not sure that is the case. Read the info on the door.

Why would they install a 400 amp main and then install 2- 400 amp breakers in the panel? Well they won't be happy.

 

[north star]

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I do not know for sure what the ct cabinet will actually

be fed with, ...could be something higher, but immediately

adjacent to the ct cabinet, this drawing is indicating (1)

400 amp. fused switch panel, ...immediately downstream

of that panelboard is (1) panelboard with a 400 amp.

service w/ 42 ocpd's & 1 400 amp. sized breaker,

...immediately downstream of that panelboard is (1)

400 amp. sized service w/ 42 ocpd's & 1 250 amp.

sized breaker, ...immediately downstream of that

panelboard is where the 45 kva, pad mounted

transformer is shown w/ (1) 200 amp. sized

panelboard with a fused switch, ...immediately

downstream of that panelboard is the last

panelboard shown......It has a 225 amp. sized

service w/ 42 ocpd's & 1 125 amp. circuit

breaker in it.

The idea of requesting service calculations is

good one......I might be able to do that!

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[Dennis]

If they are engineered drawings I am quite surprised at the setup. If the load is calculated then it doesn't matter how many panels you have as long as you don't go over the original 400 amps. I just don't know why they use 400 amp panels downstream as they are expensive. Perhaps the biggest loads are all downstream.

 

[north star]

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Dennis,

Thanks again for your input!

The drawing is only a little bit above a "paper napkin sketch"

type submittal.........It is laughable!.......But it is what I am

working with.......Most of the loads for this upsized service

is for a manufacturing / processing facility.......Lots and lots

of motors.......Their current service to this [ part ] of the

facility is already maxed out, and they DO need an

upsized service for their "already expanded operations".

Not sure if I can actually "require" engineered drawings &

load calcs. or not........As usual, it is one of "those sensitive

situations"! :banghd

FWIW, money is not an issue with the business owners.

Whatever they need to do is available.......They need

the upsized elec. service to make more money with their

operations.

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[Paul Sweet]

The NEC allows existing services to be calculated based on the maximum demand over the last 12 months plus the calculated new load. I'm at home, so I don't have a current NEC to give you a paragraph reference.

It's possible that the feeders are oversized to avoid tripping breakers if multiple motors start at the same time.

 

[Gregg Harris]

Try 220.87 Determining existing load.

 

[Dennis]

Existing service load doesn't do any good if they are adding more loads. I assume since they are upgrading that they are adding more loads. Many areas require stamped plans or for upgrade the poco may require a load calculation.

 

[chris kennedy]

+ = + =Also, an outdoor, pad

mounted transformer for the various motors onsite.

What issues do I need to be looking for?

Napkin sketch for this is unacceptable IMO. I would need to know the available fault current. You have a 480V system with motor contribution here.