Electrical subpanel question

[Anonymous-0]

Looking at an electrical distribution panel sub panel I was trying to determine what amperage it is capable of supplying.

The main panel that feeds the sub panel has two single pole breakers instead of a double pole breaker for the feed. The single pole breakers are both rated 50amps. Conductor is 6awg. No tying bar across the circuit breaker switches.
Do you add the amps to get 100amp 240vac max. Or is it 240vac 50amp max?

 

[hummingbird]

50 amps, and you need to change the breaker or put a handle tie on it.

 

[John T]

Id replace the two 50 amp single pole breakers with a two pole 50 amp as its not all that expensive or at the least have the two bar tied if you insist on their use. THIS ALL ASSUMES YOU INTEND A 120/240 VOLT SINGLE PHASE 3 WIRE CIRCUIT!!!!!!!!!!!!!!!!

The sub supply (with what you say is available) is 50 amps at 240 VAC NOTTTTTTTT 100 as you ask.

At a sub panel fed from a main DO NOT BOND THE NEUTRAL (a grounDED conductor) and EQUIPMENT GROUND (a groundING conductor) BUSSES. They shall remain isolated and independant (no ties or bonds or tie bar connections) at the sub panel

You would, therefore, run 4 wires from the main to the sub, 2 Hots, 1 Neutral (a grounDED conductor), 1 Equipment Ground (a groundING conductor)

Got it??????????????????????????????

John T

 

[Anonymous-0]

Thanks. Its not my place.

 

[buickanddeere]

Leaving the two single pole breakers instead of installing a proper two-pole breaker. Is just about enough to get you or anybody else liable should something go wrong.
A 10ft ground rod or deep buried ground plate is required out at the sub panel.Tied to the ground lug only as Ol' John T stated.

 

[SCHMUCK 2]

Two single pole breakers instead of a double pole breaker got an uncle of mine killed several years ago. Storm blew down the line going to the well at the house he and my aunt were renting and for whatever reason, he decided to put it back up himself. He located one breaker, but not the second. A friend found him early that afternoon still clutching the wire and laying in an inch or so of water. My aunt said if she had seen him, she wouldn't have realized what the problem was and the funeral home would have had to make two trips that day. DON"T allow that circuit to remain like that. I would suggest having a licensed electrician come in and inspect the installation. If some tight-wad did that, no telling what else is a death trap that you aren't seeing.

 

[Anonymous-0]

Thanks again.
It'll get resolved shortly. Right now the circuit is shutoff.
The sub panel is one foot away from the distribution panel that feeds it. 50' away from the service entrance breaker which is next to the meter. The earth ground (rod) is at the main breaker.

Its an old boat building shop. Originally built in the 1700's added onto over the years. Wire has been run many times from the looks of it. I rented a space inside it for the winter. Before I bring my equipment in I wanted to make sure there was enough power at the outlets I have access to. (There is not). I have (2) 240Vac outlets I can access. One looks to be a 20 amp plug the other 50amp fed by the breaker mentioned earlier.

Its ok for me to make upgrades or repairs I have to pay for them and there is no chance of reimbursement from what I can see. I prepaid for the winter to get the space (it has heat!) and the price/location was a good fit. Burning down the place would be a setback.

At the moment I'm thinking a 100amp breaker and wire upgrade from the distribution box to the space I'll be using. With a sub/distribution panel in my space splitting out (1) 50amp 240vac and (1) 30amp 240vac and (1) 20 amp 240vac. The equipment being run = molder,planer,unisaw,dust collection. Welder, air compressor. The 2 things that will load the system are the molder (50a) dust collection (30a). There will be a licensed electrician involved.

 

[Russ from MN]

Most single breakers that I have seen have a little hole through the handle, that is to put a pin in to pin them together whenever they feed into a common box. This is what I was told by a state inspector 34 years ago. He told me to cut off a 6d nail to the right length and drop it in, then one can't trip or be shut off without the other. The place we bought where we live now had the garage fed through 3-12 wg connected to two breakers on opposite sides of the panel, staggered,hence 220v potential, but two 110 circuits using a common neutral. This was all done by a big contractor and ok'd by the inspector. I have added a shop on so now it is all fed by a new 100a service.

 

[John T]

Its okay to use whats called a "multi wire branch circuit" which has two phase legs (L1 & L2) of 120 volts (thats 240 Line to Line) with respect to a single common shared Neutral butttttttttttttt there should be an equipment groundING conductor (often green or bare) unless its only a 2 wire circuit with no safety equipment ground.

Its a no no and very very wicked to use a Neutral (a grounDED conductor) to carry fault current (its intended for the normal return current ONLY) and/or an equipment groundING conductor to carry normal return current (its intended as a dedicated low resistance path for fault current ONLY)...

John T

 

[TomH in PA]

I thought the ground wire at the subpanel runs back to the service panel, not to another ground rod??? But I don"t claim to know the code either.

 

[buickanddeere]

Ground wire runs from the ground lug on the supply panel to the ground lug on the sub panel. The ground rod out at the sub panel also connects to the sub panel's ground lug.
Out at the sub panel there is no connection or relation between the neutral and ground.

 

[John T]

Heres how its done:

1) At the main service entrance, the Neutral (a GrounDED conductor) is bonded to a GroundING electrode conductor, typically a No 4 soft copper wire, ran to a Grounding Electrode(s)such as metallic utility pipes or a made Grounding Electrode such as driven earth ground rod(s) or buried plates etc. THATS TO BOND THE INCOMING NEUTRAL TO MOTHER EARTH USED AS A COMMON LOW POTENTIAL REFERENCE FOR THE ENTIRE ELECTRICAL SYSTEM. Out at the utility pole even the HV Primary Neutral (if one exists) is also tied to the same mother earth low voltage common reference (that copper wire you see running down the pole)

2) At the main service entrance the Neutral Buss and the Equipment Ground Busses are bonded together (often a tie bar) BUT NOTTTTTTTT AT SUB PANELS DOWNSTREAM (there Neutrals and Equipment Grounds are seperate and isolated).

3) From the main panel to sub panels, you run 2 hots (for a 120/240 single phase 3 wire service) ,,,,,,a Neutral,,,,,,,an Equipment Grounding Conductor

4) At the sub panel you can create another Grounding Electrode (such as a made one like driving rod(s) into earth or metal pipes etc) and use a gouunding electrode conductor (say a No 4 copper wire) to tie the Grounding Electrode to the sub panels Equipment Ground Buss

Got it????????????

John T Too long retired EE and rusty on this but pretty sure the above is correct

 

[Russ from MN]

3-12 wg would have a separate neutral and ground, right? My concern was that if you had 15A 110 load on each leg the neutral would have 30A on a #12 wire.

 

[36 Coupe]

Number 6 wire limits you to 50 amps.

 

[buickanddeere]

(quoted from post at 22:45:57 11/03/10) 3-12 wg would have a separate neutral and ground, right? My concern was that if you had 15A 110 load on each leg the neutral would have 30A on a #12 wire.

If wired incorrect with both breakers being supplied from the same transformer terminal. Yes the neutral will be smoking with 30A. IF wired correctly the neutral current would be zero IF the loads were identical.
Mix some inductive, reactive and high frequency noise on there from electrical/electronic power supplies and believe it or not the neutral could still become over loaded. Neutrals in modern offices are now oversized.