Tapping parallel feed Q's

[Coppersmith]

I'm adding a single phase panel right next to an existing three-phase panel that is in two sections. The two sections are connected together with two sets of parallel 3/0 CU. The sections are right next to each other. My panel will be right next to them.

I want to tap one set to power my panel. The tap is going to be very close to the lugs, probably no more than six inches away. I don't think this will unbalance the parallel feeders. What do you think?

 

[WarrMann]

Looks like it will be unbalanced to me. Yeah, it's only 6 inches, but that's 12"and a connection for the current to try to go through. Your tapped current will all go back on only the set they're connected.

Can't you install a breaker in the second section? Or add some feed through lugs at the top?

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[Coppersmith]

Looks like it will be unbalanced to me. Yeah, it's only 6 inches, but that's 12"and a connection for the current to try to go through. Your tapped current will all go back on only the set they're connected.

Can't you install a breaker in the second section? Or add some feed through lugs at the top?

Tapping is much less expensive. Both sections are full. I would have to change 4 single pole breakers to two tandems and add a 125 amp breaker. The breakers are QOB bolt-ons so they are expensive. I wasn't expecting to see parallel feeders between the sections when I planned this out.

The parallel run is only about for feet long. I suspect if I tap one wire near the lug, the current will be pulled almost equally from both wires. Current from the other wire will just have to go through the lug and back down to the tap, a total of 12 extra inches.

Not sure about adding feed through lugs. I didn't look at the other end of the panel.

 

[petersonra]

I'm adding a single phase panel right next to an existing three-phase panel that is in two sections. The two sections are connected together with two sets of parallel 3/0 CU. The sections are right next to each other. My panel will be right next to them.

I want to tap one set to power my panel. The tap is going to be very close to the lugs, probably no more than six inches away. I don't think this will unbalance the parallel feeders. What do you think?

You can't tap one of the conductors of the set, BUT you could potentially add a feeder lug to where the conductors connect to the PB and tap from there.

Or you could add two 3 pole polaris connectors.

 

[Coppersmith]

You can't tap one of the conductors of the set, BUT you could potentially add a feeder lug to where the conductors connect to the PB and tap from there.

Or you could add two 3 pole polaris connectors.

The Polaris connectors are a good idea. Wouldn't it have to be 5 pole? Two in, three out (two to section 2, one to my new section).

 

[WarrMann]

Totally understand that tapping would be cheaper than qo bolt on.

While i agree with you that it's only 12 inches, its still shorter and the current would want take the path of least resistance via the tapped conductors. Just my opinion though...

It would be interesting to put a clamp meter on after the install if you do decide to go this tap route

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[petersonra]

The Polaris connectors are a good idea. Wouldn't it have to be 5 pole? Two in, three out (two to section 2, one to my new section).

My inclination would be to take 1/2 or 3/4" of insulation off the existing connectors in the second PB a few inches from the end of the conductors and slide the Polaris connector there so the conductors are continuous through the Polaris connector to the lugs on the PB.

 

[WarrMann]

The Polaris connectors are a good idea. Wouldn't it have to be 5 pole? Two in, three out (two to section 2, one to my new section).

I don't think That's not going to save you too much versus a few breakers and the time it will take to refeed.

What size wire are you hitting the new panel with? Could that be done in parallel?

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[WarrMann]

My inclination would be to take 1/2 or 3/4" of insulation off the existing connectors in the second PB a few inches from the end of the conductors and slide the Polaris connector there so the conductors are continuous through the Polaris connector to the lugs on the PB.

That's going to create a mess of lugs at the panel.

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[petersonra]

That's going to create a mess of lugs at the panel.

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maybe. for the size wires the OP is talking about 3 pole polaris connectors are not huge.

 

[Coppersmith]

It would be interesting to put a clamp meter on after the install if you do decide to go this tap route

Well, interestingly, I measured the amps on each of the parallel conductors (before my install) expecting each pair to be identical. They were not. The panel is lightly loaded during the day (it has mostly outside lighting) with each conductor carrying about 5-6 amps. There are a difference of about .5 amps between the pairs.

 

[WarrMann]

Well, interestingly, I measured the amps on each of the parallel conductors (before my install) expecting each pair to be identical. They were not. The panel is lightly loaded during the day (it has mostly outside lighting) with each conductor carrying about 5-6 amps. There are a difference of about .5 amps between the pairs.

The .5 difference is likely in your meter. Check with a heavier load, and move the wire around inside the clamp.

My (current) fluke has an accuracy of 2% for amps, and two digits after the decimal. I know for a fact that where i hold the wire inside the clamp effects the reading. It prefers the wire to be centered

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[tkb]

The Polaris connectors are a good idea. Wouldn't it have to be 5 pole? Two in, three out (two to section 2, one to my new section).

You would need to tap both of the parallels.
1/0 is the minimum parallel size.

 

[retirede]

While the Polaris connector is probably the best idea, it might be possible to replace the parallel 3/0s with a single conductor. It would probably need to be 600 which means changing out the lugs.

 

[Coppersmith]

You would need to tap both of the parallels.
1/0 is the minimum parallel size.

Based on Bob's comment, I think this would be compliant. The parallels are 3/0 CU. The tap could be any size. In this case it will be 1/0 AL. Note that the feeders come together in the Polaris connector and then separate again until the lug. Or I could change the wire between the Polaris and the lug to a very short piece of 600 MCM. Not sure how the supply house would react to me ordering a 1 foot piece.

 

[tkb]

Based on Bob's comment, I think this would be compliant. The parallels are 3/0 CU. The tap could be any size. In this case it will be 1/0 AL. Note that the feeders come together in the Polaris connector and then separate again until the lug. Or I could change the wire between the Polaris and the lug to a very short piece of 600 MCM. Not sure how the supply house would react to me ordering a 1 foot piece.

Like I said, he needs to tap both of the 3/0 parallels, but if he ran parallel taps the min size would be 1/0.
I never said that the tap had to be a min of 1/0.

If the feeder was connected as in your sketch, it looks like it would be compliant with a single tap. The sizing is governed by the tap rule.

 

[masterinbama]

Why not change the panel lugs to 3 holes and be done with it?

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[tkb]

I would either change the lugs, or use a hypress lug under the mounting bolt of the existing lugs.