Backfeeding

[mstrlucky74]

What exactly is meant when you back feed a panel or dist board? If someone couild give an example involving two existing dist boards . Thanks

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[infinity]

In your case it means that they want you to provide an alternate feed to the panel so the existing permanent feed can be disconnected.

 

[mstrlucky74]

In your case it means that they want you to provide an alternate feed to the panel so the existing permanent feed can be disconnected.

This is what I don't understand and the backfeeding comment was made by someone in my office. Have a main swbd feeding a 2nd switchboard using 3 sets of 750. He said if we disconnect one of the sets it would be backfeeding In my mind of you disconnect one of the sets the 2nd board is dead!

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[mstrlucky74]

And this brings me to my other point where I tried to post the pics. If you are to remove ONLY the feeders between these two boards as they are being replaced the only way you could keep the 2nd board live while doing this is to temp it out and that could only be done from another OCPD or dist board etc. Correct?

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[Strathead]

This is what I don't understand and the backfeeding comment was made by someone in my office. Have a main swbd feeding a 2nd switchboard using 3 sets of 750. He said if we disconnect one of the sets it would be backfeeding In my mind of you disconnect one of the sets the 2nd board is dead!

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I am sure you misunderstood what he was saying. That said, if you were to disconnect one set, the 2nd board would still be energized from the other two sets, it just wouldn't have the ampacity of the third set available. If you took one set, disconnected it and hooked it up to a different source that might be what is referred to. But I don't call that backfeeding. Terms can be used differently, but I would merely call that an alternate temporary feed. For me, the term "backfeed" is to take a panel and instead of bring the power in to the bus connected main breaker, or main lugs, you install a breaker in a branch slot (or a terminal block made for this) and hook the feeder up to it.

 

[retirede]

For me, the term "backfeed" is to take a panel and instead of bring the power in to the bus connected main breaker, or main lugs, you install a breaker in a branch slot (or a terminal block made for this) and hook the feeder up to it.

This is my definition as well.

 

[mstrlucky74]

I am sure you misunderstood what he was saying. That said, if you were to disconnect one set, the 2nd board would still be energized from the other two sets, it just wouldn't have the ampacity of the third set available. If you took one set, disconnected it and hooked it up to a different source that might be what is referred to. But I don't call that backfeeding. Terms can be used differently, but I would merely call that an alternate temporary feed. For me, the term "backfeed" is to take a panel and instead of bring the power in to the bus connected main breaker, or main lugs, you install a breaker in a branch slot (or a terminal block made for this) and hook the feeder up to it.

That's what I was thinking..energized but with less amapacity and that could be a problem depending on the connected loads.

If you backfeed the way your describing how to "liven" up the entire board by bringing the feeder to a branch breaker instead of main breaker or lugs? Or are you saying by doing this your not "livening" the entire board/panel and just that breaker?

Thanks.

 

[Smart $]

This is what I don't understand and the backfeeding comment was made by someone in my office. Have a main swbd feeding a 2nd switchboard using 3 sets of 750. He said if we disconnect one of the sets it would be backfeeding In my mind of you disconnect one of the sets the 2nd board is dead!

I think what he meant is if you disconnect one set from the breaker in the source swbd, the disconnected set will still energize when the breaker energizes the remaining sets. The disconnected set is being "back fed" from because it is still connected to the other two sets ate the load swbd. You have to disconnect the one set at both source and load swbd for it to dead when source breaker is energized.

That said, Code compliance must be maintained even during temporary situations. To energize just two sets of three existing will likely require a downsizing of the source-end breaker rating and verification the calculated load does not exceed the circuit rating.

 

[Strathead]

I think what he meant is if you disconnect one set from the breaker in the source swbd, the disconnected set will still energize when the breaker energizes the remaining sets. The disconnected set is being "back fed" from because it is still connected to the other two sets ate the load swbd. You have to disconnect the one set at both source and load swbd for it to dead when source breaker is energized.

That said, Code compliance must be maintained even during temporary situations. To energize just two sets of three existing will likely require a downsizing of the source-end breaker rating and verification the calculated load does not exceed the circuit rating.

I agree this might be. Either way, the OP is misunderstanding something that was said.

 

[Strathead]

That's what I was thinking..energized but with less amapacity and that could be a problem depending on the connected loads.

If you backfeed the way your describing how to "liven" up the entire board by bringing the feeder to a branch breaker instead of main breaker or lugs? Or are you saying by doing this your not "livening" the entire board/panel and just that breaker?

Thanks.

Again, I will state that "backfeed" is going to be used differently by different people since it has no official definition in the code. The only reason I can think that you would do a temp backfeed would be so that you could transfer back and forth between the two sources quickly. I would not do this nor encourage it without a kirk key or other infallible lockout system in place. Backfeed as I describe it is generally done to provide main breaker overcurrent protection to a panel that is a main lug only, in lieu of a separate fused disconnect or enclosed circuit breaker. It is common in smaller panels, and I believe even panels like a Square D iLine can be backfed, but there would be special mounting hardware required to prevent the breaker from being removed and usually the spaces opposite the breaker on the bus are permanently blocked out so they can't be used.

 

[mstrlucky74]

So we are replacing feeders between 1600a switch in main switchboard to PP-HA and between PP-HA and PP-HB. We are re-using all conduits. Question is how do you keep PP-HA and PP-HB live(or minimal downtime) while replacing these feeders?

 

[Strathead]

So we are replacing feeders between 1600a switch in main switchboard to PP-HA and between PP-HA and PP-HB. We are re-using all conduits. Question is how do you keep PP-HA and PP-HB live(or minimal downtime) while replacing these feeders?

In my opinion, with the atmosphere and NFPA 70E today, you don't. Keeping them live while you are changing the feeders would be a violation of NFPA 70E unless it could be shown that a loss of life is a potential problem and there is no way around it.

 

[mstrlucky74]

In my opinion, with the atmosphere and NFPA 70E today, you don't. Keeping them live while you are changing the feeders would be a violation of NFPA 70E unless it could be shown that a loss of life is a potential problem and there is no way around it.

Have to look at NFPA 70E. Why couldn't a temporary power situation be implemented to keep PP-HA power up for most of the feeder replacement. Yes it would have to be shutdown when disconnecting and terminating.

 

[Smart $]

Have to look at NFPA 70E. Why couldn't a temporary power situation be implemented to keep PP-HA power up for most of the feeder replacement. Yes it would have to be shutdown when disconnecting and terminating.

To pull new feeders into and out of PP-HA will require getting into PP-HA. You can't do that while it is energized without good reason... and financial burdens are not justifiable.

 

[Strathead]

Have to look at NFPA 70E. Why couldn't a temporary power situation be implemented to keep PP-HA power up for most of the feeder replacement. Yes it would have to be shutdown when disconnecting and terminating.

and pulling the conductors in and out. In many ways I actually consider this the most likely operation to create a hazard.

 

[Strathead]

To pull new feeders into and out of PP-HA will require getting into PP-HA. You can't do that while it is energized without good reason... and financial burdens are not justifiable.

To add to Smart, you can try to read NFPA 70E, but what he said is the part I was getting at. And the verbage of that huge book is hard to get that.

 

[mstrlucky74]

To pull new feeders into and out of PP-HA will require getting into PP-HA. You can't do that while it is energized without good reason... and financial burdens are not justifiable.

You pull feeder to a box close then pull in and terminate while it's shutdown.

 

[Strathead]

You pull feeder to a box close then pull in and terminate while it's shutdown.

You said you were using the same conduits didn't you?

 

[mstrlucky74]

You said you were using the same conduits didn't you?

Aaaahhhh I was thinking about the temp but yes obviously we would have to pull the new/perm through the live board which I guess is no no.