Temping Out Panel

[garbo]

So I may have to temp out the secondary side(of xfrmr) panel while we shut down to disconnect/reconnect.

What would be the most practical way to temp the panel out? Thanks

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I retired from a large hospital and several times a year they would have major renovations on portions of the 12 floor building. This would involve relocating the feed for 480 to 120/208 transformers. Luckily most existing transformers were lightly loaded and could accommodate back feeding another panel. We would install a three pole circuit breaker and run 4/0 SER cable from panel that was going to loose power to nearest panel. Would install A LOTO on panel main breaker with a shackle and had our hospital electrician & electrical contractor install a lock. We would use a rotation meter to make sure any 3 phase motors would operate in the correct direction.

 

[kwired]

I retired from a large hospital and several times a year they would have major renovations on portions of the 12 floor building. This would involve relocating the feed for 480 to 120/208 transformers. Luckily most existing transformers were lightly loaded and could accommodate back feeding another panel. We would install a three pole circuit breaker and run 4/0 SER cable from panel that was going to loose power to nearest panel. Would install A LOTO on panel main breaker with a shackle and had our hospital electrician & electrical contractor install a lock. We would use a rotation meter to make sure any 3 phase motors would operate in the correct direction.

That is basically what I have been trying to tell OP to do.

 

[Alwayslearningelec]

I have connected a temporary feed in parallel, just using some SER or MC cable, and then disconnected the original feed, thus having no loss of power at all. Obviously that involves hot work and weather that is feasible will depend on who is doing the actual work. Of course it could be not hot with just a minute or two outage also. Is there another panel near by? Simplest would be to come off of a 100A breaker if there is space available.

Can you explain how connecting in parallel would work, thank you.

 

[electrofelon]

Can you explain how connecting in parallel would work, thank you.

Say you have panels A and B. A is getting it's permanent feed redone. Put a 100 amp breaker in each panel (or however you are going to make some temp connections). Run a feed between those two breakers. Check phasing, energize. Remove and reinstall feeder to panel A, turn off breakers and remove temp feed.

Bonus for having some fun with your apprentice or the new guy (not that I would be having them do hot work). Hide a delta -wye transformer with a 1-1 voltage ratio somewhere to create a 30 degree phase shift, ask apprentice why it's taking him so long to phase out that temp feed

 

[Alwayslearningelec]

Say you have panels A and B. A is getting it's permanent feed redone. Put a 100 amp breaker in each panel (or however you are going to make some temp connections). Run a feed between those two breakers. Check phasing, energize. Remove and reinstall feeder to panel A, turn off breakers and remove temp feed.

Bonus for having some fun with your apprentice or the new guy (not that I would be having them do hot work). Hide a delta -wye transformer with a 1-1 voltage ratio somewhere to create a 30 degree phase shift, ask apprentice why it's taking him so long to phase out that temp feed

Thanks. But I'm confused. So the point is to keep the loads in panel A energized the entire time correct? You say your now temping out those panel A loads with a temp feed from panel B 100A breaker to 100A breaker in panel A? Ok of I'm correct with the scenario then where I'm confused is how you get the 100A breaker in panel A to "energize" all the branch circuits in panel A. Thanks Electro

 

[augie47]

You put a 100 amp breaker in both panels and tie them together making sure you phase correctly.
Back feed A from B and then turn off and disconnect the original feed to A main until you re-feed it from the new transformer
Your journeyman should be able to handle it if you supply him the right breakers/wire.

 

[Alwayslearningelec]

You put a 100 amp breaker in both panels and tie them together making sure you phase correctly.
Back feed A from B and then turn off and disconnect the original feed to A main until you re-feed it from the new transformer
Your journeyman should be able to handle it if you supply him the right breakers/wire.

Understood but I’d like to understand how this works . I get the concept but not following exactly how panel A branch loads
Remain active . I get the scenario about the 2 100a breakers .

 

[electrofelon]

Understood but I’d like to understand how this works . I get the concept but not following exactly how panel A branch loads
Remain active . I get the scenario about the 2 100a breakers .

You have two feeds. Basically you turn on the temp feed before de-energizing the feed to be removed. When you turn on the temp feed, it will take about half the load off the other feed (exact amount will depend on the relative impedances). Then you can remove the feed to be moved and all the load will be on the temp feed.

Just reiterating that this involves hot work and it may be against some companies' policy and/or some people will not be comfortable doing it . Personally I would (and have) done it on a 208 system but probably wouldn't with 480 unless absolutely necessary - and maybe not even then

 

[Fred B]

You have two feeds. Basically you turn on the temp feed before de-energizing the feed to be removed. When you turn on the temp feed, it will take about half the load off the other feed (exact amount will depend on the relative impedances). Then you can remove the feed to be moved and all the load will be on the temp feed.

Just reiterating that this involves hot work and it may be against some companies' policy and/or some people will not be comfortable doing it . Personally I would (and have) done it on a 208 system but probably wouldn't with 480 unless absolutely necessary - and maybe not even then

Just make sure your phases all line up. (or you get a big BOOM). It would look like something similar to a PV back-feed system.
To OP: example to how possible, simply go to a panel with a volt meter, meter between to points of A phase buss, you get 0 volts, same thing if you have two power sources and on same phase you would read zero volts. So you would be able to have both on before shutting one off.

Safest is to deenergize system. Why is it "critical" to not shut down even for a little bit to allow for changing out the feeds? NFPA70E has some very specific criteria as to energized work allowance and what is considered "necessary". Inconvenience to the customer I don't think qualifies.

 

[Alwayslearningelec]

Say you have panels A and B. A is getting it's permanent feed redone. Put a 100 amp breaker in each panel (or however you are going to make some temp connections). Run a feed between those two breakers. Check phasing, energize. Remove and reinstall feeder to panel A, turn off breakers and remove temp feed.

Bonus for having some fun with your apprentice or the new guy (not that I would be having them do hot work). Hide a delta -wye transformer with a 1-1 voltage ratio somewhere to create a 30 degree phase shift, ask apprentice why it's taking him so long to phase out that temp feed

So sorry for not fully grasping. Staying with the panel A/B scenario.
1. Panel A branch loads need to stay active. The main feed to panel A is being replaced.
2. Panel B has a spare breaker or you add one to feed a breaker you install in panel A, correct?
3. How does the breaker you install in panel A energize the branch loads in panel A if they are already fed by the main breaker(if main breaker) in panel A? This is where I'm confused.

 

[augie47]

Try this:
Think of a car battery being removed.. lets call it battery "A". You take a second battery , "B", and hook jumper cables to it and to the connectors on battery "A". At that point the car is getting power from both batteries. You slip the connectors off battery "A" (leaving the jumpers from B connected) and the car is still getting power from "B"so there is no loss of power to the car..
You then replace A, reconnect the connectors to A and remove the cables and B.
That help ??

 

[electrofelon]

the panel A temp breaker is being backfed.
When you flip the breakers on, you have two feeds in parallel - just like if you had parallel conductors but of course in the case not in the same raceway. It only works if the two sources are "synched" (which they would be unless you had something weird going on like a D-Y transformer on one but not the other, or a generator, UPS or inverter). Obviously you have to phase the connections correctly. Before throwing the panel A temp breaker I would meter from the bus to breaker terminal of each pole and assure I have 0 volts.

 

[garbo]

the panel A temp breaker is being backfed.
When you flip the breakers on, you have two feeds in parallel - just like if you had parallel conductors but of course in the case not in the same raceway. It only works if the two sources are "synched" (which they would be unless you had something weird going on like a D-Y transformer on one but not the other, or a generator, UPS or inverter). Obviously you have to phase the connections correctly. Before throwing the panel A temp breaker I would meter from the bus to breaker terminal of each pole and assure I have 0 volts.

 

[Alwayslearningelec]

Try this:
Think of a car battery being removed.. lets call it battery "A". You take a second battery , "B", and hook jumper cables to it and to the connectors on battery "A". At that point the car is getting power from both batteries. You slip the connectors off battery "A" (leaving the jumpers from B connected) and the car is still getting power from "B"so there is no loss of power to the car..
You then replace A, reconnect the connectors to A and remove the cables and B.
That help ??

Yes a little, thank you. I do get the concept but not how it technically works.
Staying with the panel A/B scenario. Am I correct in saying?

1. Panel A is getting temporarily fed by panel B?

So a main breaker feeds the panel is a typical situation.

In the panel A/B scenario the new breaker install in panel A would now be feeding the panel(branch loads)? How would that work if there is already a main breaker feeding the panel?

Thanks.

 

[garbo]

We were not allowed to have a panel paralleled feed for a few seconds unless both panels were feed by the same transformer. We had several phase indicating meters and often found both 480/277 & 120/208 volt panels that had the conductors marked ( such as BOY = Brown Orange Yellow ) not identical meaning the Brown wire in panel "A" is identical to Orange in panel " B ". Years ago we were having problems with automatic tie breaker not paralling when we lost one of the 13,200 volt utility services. The company that serviced the equipment thought the two incoming services were not in phase and the Utility company said there side was okay. Finally the ultility shut down one of the services for a day and problem was solved.

 

[kwired]

Yes a little, thank you. I do get the concept but not how it technically works.
Staying with the panel A/B scenario. Am I correct in saying?

1. Panel A is getting temporarily fed by panel B?

So a main breaker feeds the panel is a typical situation.

In the panel A/B scenario the new breaker install in panel A would now be feeding the panel(branch loads)? How would that work if there is already a main breaker feeding the panel?

Thanks.

The electricity doesn't care what is a main breaker and what is not. Close both breakers in the described situation and you created a parallel path and current divides between the two paths. Open one of them and all current is forced to take the path through the closed breaker. So close the original main and now all current is taking the alternate path you provided. The supply side of main is still hot, but we are presuming you can open it's supply side pretty easily which totally isolates it so you can work on it deenergized.

Keep in mind if the panel you are temporarily feeding has more than 100 amps of load at the time your temporary 100 amp breaker will not hold for very long and will trip. The 100 amp breaker was a suggestion only because it is normally something easily obtained that will be easy to just plug on to any position in the panel, but if you have more than 100 amps load when attempting to do this, it probably not going to work uninterrupted, you need to have users on limited loading while performing this yet the process will allow non interruption for what load they are using.

 

[electrofelon]

The 100 amp breaker was a suggestion only because it is normally something easily obtained that will be easy to just plug on to any position in the panel, but if you have more than 100 amps load when attempting to do this, it probably not going to work uninterrupted, you need to have users on limited loading while performing this yet the process will allow non interruption for what load they are using.

This might work for a situation where the load is over 100

Not Authorized NorthEast Electrical

www.needco.com

That might take up 6 spaces, but there is usually a 125A version that I think is only 3. Not as good as a breaker though as it is more stuff you have to do hot.

 

[kwired]

This might work for a situation where the load is over 100

Not Authorized NorthEast Electrical

www.needco.com

That might take up 6 spaces, but there is usually a 125A version that I think is only 3. Not as good as a breaker though as it is more stuff you have to do hot.

There are other manufacturers that have breakers as well as sub feed lugs that take 2 spaces per pole as well. I only mentioned the typical 100 amp breaker because it is something more readily available in most cases. The sub feed lug kit is a little more risky because you will be making at least one connection that is live where with the breaker you can make it up while not energized then flip the switch.

 

[Alwayslearningelec]

Sorry guys. I'm still not clear on back feeding in this scenario. And exactly how the panel getting the main feed removed, receives it power.

I will try to be clear and concise.

1. Transformer secondary is feeding panel A.
2. Transformer is being replaced.
3. Panel A needs to remain live.
4. Panel B is in the room and can temporarily feed panel A if spare breaker available or room for one. CORRECT????
5. One option, that IS NOT back feeding, is to run a temp feeder from panel B to panel A. Quickly disconnect panel A main feed and hook up temp feed. There would be downtime, but it would be minimal. Is this possible scenario I explain CORRECT?
5. Now the back feed scenario. Run temp feed from panel B to a newly installed breaker in panel A, CORRECT? When main breaker in Panel A is turned off then you turn on panel B breaker, CORRECT?
6. If #5 is correct does the newly installed breaker in panel A feed/energize the loads in this panel? I'm thinking it's just a branch breaker as the main breaker is still installed.

Thank you very much.

 

[petersonra]

You are going to have some down time no matter what.

My suggestion is install new transformer and run conduit and wires to vicinity of old transformer. Turn off power for ten or fifteen minutes while you disconnect old transformer and tie in new one.