More wiring???

[fullbore1]

Figuring full load at 55 amps (bigger elements) L1 and L2 on separate breakers. So looking at the following diagram, if L1 is wired directly to the breaker through the plug and L2 is through the SSR does the SSR see the full current (55 A) or only the current supplied through the L2 (27.5A) leg? Also what good is the 4 wire system if the neutral and the ground are tied in the breaker box?

[Brintiff]

Each leg is going to pull 50 amps (at 240) , common mistake is to think a 50 amp device draws 25 amps per leg. Your SSR is going to see 50 amps on the one leg. Why are you not breaking both legs with the SSR? Maybe it's an SSR thing? I refuse to use them, I want something that 99.9% of the time is going to fail in the "open" position, like a contactor, having an SSR fail and stay closed would keep me awake at night.

The neutral and ground only terminate in the same spot if it's in the "primary means of disconnect". What do you mean that L1 and L2 are on separate breakers? They MUST be on one 2 pole breaker.

[ed_denu]

A good target for ssr's, breakers, etc. is no more than 80% rated load. Pushing 55 amps thru a 60 amp ssr is probably going to result in a short ssr life span, even if you have an extremely good heatsink.

While the neutrals and grounds(earth) both terminate at the main service panel(first disconnect) they serve two distinct functions. At subpanels, such as those in garages and detached building they remain separate. The neutral connection will carry return current from any device using 120 volts, such as the pid, lights, fan, etc. A Ground represents an electrical path, normally designed to carry fault current when a breakdown occurs within electrical equipment.

Brintiff, SSR's typically are single pole, so only one leg of the 240 volt supply is switched. All ovens, etc. should have a master disconnect that disables the oven when not in use. Concerns about failed close ssr's can be easily alleviated by using a high temperature alarm.

[fullbore1]

The diagram was for flow purposes only. I have a 75 amp SSR and needed to know if I could use 30A breakers or needed 60's also it looks like I need 6AWG wire for this correct?

Yes, I will use a master disconnect and an over temp alarm.

[ed_denu]

As Brintiff pointed out, you need a double breaker of sufficient capacity to support the load. I'm not sure what the question is about using 30 amp breakers? If your load is 55 amps, you need a 70 amp double pole breaker and #4 wire.

[fullbore1]

In the past there I have seen two breakers tied together at the shut off switch for 220V supplies. But as pointed out I will get the double pole 75A. Thanks. The 30A was in the 30+30=60A thought pattern.

[PhredAre]

Ed, The neutral and the ground are tied together in the main panel but I believe in a sub panel they are to be isolated from one another to prevent ground currents from running on the neutral in the avent that the ground fails.Just a thought. Fred

[ed_denu]

Originally Posted by PhredAre

Ed, The neutral and the ground are tied together in the main panel but I believe in a sub panel they are to be isolated from one another to prevent ground currents from running on the neutral in the avent that the ground fails.Just a thought. Fred

Fred, You are correct. I thought I noted that in my first post, but perhaps I wasn't clear. A very good point either way.

[philipd]

Dumb question here: why doesn't a 240 circuit have a neutral? Does one leg act as a neutral for the other leg?

[SCOTTRODS]

Originally Posted by philipd

Dumb question here: why doesn't a 240 circuit have a neutral? Does one leg act as a neutral for the other leg?

It's not a dumb question.... It is apparent there's not much electrical knowledge in your life though. That's nothing to be ashamed of at all.

a 220/240 circuit is 2 110/120 hot legs, and a neutral (3 wire),.... in later model systems, there is also a ground (4 wire).....

<edit> I forgot to point you to the first post - it shows a 4 wire set-up <end edit>