Request help fixing confusing 1960 install; 120/240 1 PH panel fed by 208Y/120 3 PH

[petersonra]

If he goes to step up step down, he could ground one end of the high side and use that exception to bond both ends of an SDS and thus only need 2 conductors (if by chance 1 is bad but 2 are good).

What exception would allow that? He still needs an egc

 

[electrofelon]

What exception would allow that? He still needs an egc

I forget exactly, 230 (A)(2) exception or something like that. He could use the grounded conductor as the EGC. This would be if he makes it an SDS using transformers.

 

[synchro]

A suggestion is to put a load on the field panel and measure the voltage drop when going from an unloaded to loaded condition. That would give you a number to predict how much load current it can support with voltage drop that's acceptable for your application. Balancing the kVA of 120V loads between L1-N and L2-N will result in less voltage drop than putting all of that kVA on just one phase with a 208/120V supply. But there will still be some voltage drop on the neutral even with balanced loads because of the 120 degree phase relationship.

Also, with a L-N load on one phase, use a clamp meter on the line and neutral conductors that feed the bus inside of the field panel and compare their current readings. Any reduction in current on the neutral wire would indicate the portion of the current that's flowing on the conduit or other ground path. For example, if the neutral current is half of the line current then the impedance of the EGC path must be the same as that of the neutral conductor because they are conducting equal currents. This is assuming there's a N-G bond in the field panel.

 

[Installer]

Thank you all for your help.
1. I only need 3 circuits 120 VAC at the receiving end. Each of our loads is 5 A at the most, but I guess I have to rate it as 45 amp service at the receiving end because breakers only come in 15A or 20 A sizes.
2. Right now I have 2 120 VAC hots and One neutral coming from a 3 Phase breaker without a Ground conductor going back to the source.
3. I'd like to use the conductors as 2 H and 1 G for 208 VAC single phase as a Transformer and derive a neutral locally.
4. Just curious can I keep the two H and 1 N conductors we have now, use a Transformer, and derive a Ground because we are now separately derived locally or is that illegal?

 

[jim dungar]

Your existing installation is not 'illegal', it is simply not up to the current code. It is probably your choice to upgrade it or not.

You would need to size your transformer based on the expected total load not on the sum of the breaker handle ratings.

 

[LarryFine]

1. I only need 3 circuits 120 VAC at the receiving end. Each of our loads is 5 A at the most, but I guess I have to rate it as 45 amp service at the receiving end because breakers only come in 15A or 20 A sizes.

You could use a single 20a feeder for three 5a loads, even with three 15a breakers.

 

[robertd]

Thank you all for your help.
1. I only need 3 circuits 120 VAC at the receiving end. Each of our loads is 5 A at the most, but I guess I have to rate it as 45 amp service at the receiving end because breakers only come in 15A or 20 A sizes.
2. Right now I have 2 120 VAC hots and One neutral coming from a 3 Phase breaker without a Ground conductor going back to the source.
3. I'd like to use the conductors as 2 H and 1 G for 208 VAC single phase as a Transformer and derive a neutral locally.
4. Just curious can I keep the two H and 1 N conductors we have now, use a Transformer, and derive a Ground because we are now separately derived locally or is that illegal?

As others have said, there is nothing wrong with your existing installation. It meet code when it was installed. If you really want to do something sink two ground rods so you have a GES at the remote structure.

 

[synchro]

Thank you all for your help.
1. I only need 3 circuits 120 VAC at the receiving end. Each of our loads is 5 A at the most, but I guess I have to rate it as 45 amp service at the receiving end because breakers only come in 15A or 20 A sizes.
2. Right now I have 2 120 VAC hots and One neutral coming from a 3 Phase breaker without a Ground conductor going back to the source.
3. I'd like to use the conductors as 2 H and 1 G for 208 VAC single phase as a Transformer and derive a neutral locally.
4. Just curious can I keep the two H and 1 N conductors we have now, use a Transformer, and derive a Ground because we are now separately derived locally or is that illegal?

...



Perhaps you're just showing this transformer spec for illustration purposes which is fine. But you'll need a larger unit to support 1.8 kVA from three 5A 120V loads.

 

[electrofelon]

4. Just curious can I keep the two H and 1 N conductors we have now, use a Transformer, and derive a Ground because we are now separately derived locally or is that illegal?

You wouldn't derive a ground. A transformer can be used to derive a conductor that could then be made a grounded conductor. You already have a grounded conductor to run your 120 loads and that conductor can also serve as a low impedance path back to the source. I see no reason to change anything other than add a GES at the remote structure of there isn't one.

 

[Little Bill]

If it ain't broke, don't fix it!

 

[learningfast]

It's hard to tell but It looks like the black wire/ reidentified with green tape is going out the bottom of the box probably to a ground rod? You have 2 empty breakers, like the others, I don't see a problem.