3 Wire Vs 4 Wire Feeder

The panel itself is not grounded nor are any of the circuits grounded.

3 wire vs 4 wire feeder. When you say 3 wire 220v line i would assume that you have 2 insulated copper wires and 1 bare copper wire. It goes like this. But if it feeds something else that pulls a lot of power then i would advise having that fourth whiteneutral wire in the circuit feeder cable. The neutral and ground are not bonded in the subpanel.

However without a 4 wire feed. 3 wire was fine under the nec until just a few years ago basically each feed to a separate building was viewed and wired like its own service drop with two hot legs and a neutral but no ground distinct from the neutral. If you have an imbalance in your main panel this can cause a backfeed on your neutral that i understand. You may guess that 40 awg is just another way to say 4 awg youd be wrong.

Im aware that a 3 wire feeder without a dedicated ground used to be allowed between two detached buildings provided no other conductive paths like plumbing or a phone line exists between the buildings which the metal conduit already violates. Service equipment 100a at the outside garage wall. 4 awg 3 awg 2 awg 1 awg 0 awg 00 awg 000 awg 0000 awg. But maybe the question was not referring to transmission systems.

But that perked my interest in the question of 3 vs 4 wire feeds to outbuildings. The reason for this being if there is something that runs on 120 volt then it needs a neutral and without the fourth wire in the feeder cable then the ground becomes a neutral and a current carrying conductor. From 2008 and beyond a 4 wire feeder is required. All three wires are 4 awg.

In this setup if a hot wire coming in contact with the non current carrying parts of the electrical system outlet covers panel covers etc the 4th ground conductor will provide a low resistance patch back to the. 4 wire versus 3 wire subfeed. These should be coloured black and red. If there is an old 3 wire feeder you must bond the neutral just like in a service and connect the gec from your grounding electrodes to the neutral.

With a 4 wire feed to a subpanel your neutral and ground wires are both connected to the neutral in the main panel but at the subpanel they are isolated on seperate bars. The current nec code requires a 4 wire feeder so there is a separate grounding connector between the main and sub panels. Then you see numbers like 40 awg. This new panel 60a at the inside garage wall had the 3 wire feed.

This panel was fed by 3 wires from the service equipment. Up until the 2008 nec code cycle 3 wire feeders were permitted if there were no metallic paths between the two structures. This new panel supposedly was recently installed and permitted. That is 0000 can also be called 40 or like 4 zeros or in wire nerd speak.

Most 3 phase transmission systems over long distances operate on 3 wires to eliminate the cost of the 4th wire.