Electrical Feeders and Panels

It would be wise to ensure that only one of the two feeds, or neither of them, can be connected to panel C at any time. How that is to be effected can vary, though one commonly-found way is with a Castell Key (usual disclaimer) and two locks for it.

In starter panel C, after the disconnector (downstream), we have two contactors to ensure that only one feed is connected to the loads.

1) But my doubt is, if the load requires only 160A, then does the following have any impact:

• if the upstream feeder from Panel A being 200A and the downstream disconnector in Starter panel C being 160A

or

• vice versa (upstream feeder 160A and downstream disconnector 200A)

2) Is the switch disconnector only for isolation purpose? Becos I saw in the above catalog link that the switch disconnector takes care of the short-circuit fault also.

Pls clarify.

Thank you

Provided the two supplies to C cannot be both connected at the same time, then put a minimum 160A-rated isolator in the 160A feed, and a minimum 200A-rated isolator in the 200A feed. Now, it may be that 2 x 200A-rated isolators make the tidiest solution aesthetically....

If I put 160A rated isolator (downstream in starter panel) in the 200A feed (coming from main switchboard), is there any problem, becos now the starters are already here.

I was thinking as the load is less than 160A, the feeder from switchboard being higher rated (200A) would not pose a problem.

Pls clarify.

I don't know anything about the technical aspects of this, but if there are to be two two feeds into a single enclosure, stick on a prominent 'This panel fed by more than one supply'.

The US Electrical Code (and OSHA?) require it. And so does a proper sense of precaution.

DZ

Good answer. This kind of thing can be lethal. There is nothing wrong with supplying an alternative feed (providing reasonable electrical precautions are taken) but it is important that maintenance people are aware that there are two feeds. The standard warning is so ubiquitous (and often interpreted to mean that the other supply is "just" 120 VAC control power, etc.) that it is a good idea, I think, to be specific with the warning label.

Looking at the connected load, 160A Isolator shall serve the purpose provided you don't have any future expansion plan in Starter Panel.

As previously stated SAFETY, SAFETY and more SAFETY.

I don't see a problem with running your two loads thru a single disconnect that is properlly rated. What I don't see is how do you determine which feed is used.

I'm guessing not assuming (everybody knows what happens when you assume), that if feed A fails you will manually remove the cables from feed A and the starter. Move said cables to feed B and the starter?

If that is the case how far away is the main feed from the starters and disconnect?

Please deduct points for poor grammer

Mike,

You never want to hook 2 seperately derived systems to the same device without using a transfer switch. This eliminates backfeeding and sloves the safety issue.

By my calculation the starter panel "C" requires a 200A feed.

The information you gave only covers 3 motors: (2) 65A and (1) 4A=134A; 134Ax 175%=234A. This doesn't include voltage drop due to internal resistance of the feeders x Ft. of run and whether in a raceway or cabletray.

Hi,

Thanks for all the comments.

KKK - thanks for answering my question. I would appreciate if others too to comment on my queries raised under item 4. (sorry posted anonymously)

PWslack - appreciate your inputs too.

Dread, Mike, Blink - A 6P disconnector is used to enable the two supplies but there is a contactor is each of the circuit, which ENSURES that only one contactor is on anytime.

Regarding the reply from noshorts, can anyone comment 134 A is my total load. Do I really need 200A feed? The load will only be starting one at a time.