Three wire cicuit

bill_105

I know what happens when you lose the common. If you lose the common, you lose the appliance. If one of the circuits has a huge draw, as in tripping the breaker all the time, and the other circuit is very small , would this resemble losing the common?

My two outside cabins have worked fine for 14 years but then a huge amp load took place at one and now I have a broken freezer full of fish in the other.

Jamie Hall

Aren't sparkies fun?

Might I ask what caused the huge amp draw?  If the breaker trips once, no sweat.  In my view, if you've disconnected or turned off whatever it was you were using and it trips again, find out why.



There is one way in which a huge amp draw on one side of a three wire 120/240 type circuit can cause a real problem on the other side: if there is some resistance in the common, as from a weak or corroded connection.  It won't unbalance the voltage as badly as no common at all, but a resistance of, say, only 2 ohms will raise the voltage on the unloaded side by 30 to 40 volts, depending on the circuit breaker rating, which could well be enough to fry a freezer.



I'd want to check all the connections and wiriing for mechanical and electrical soundness...

Techman

Tripped breaker

Did you have an amp meter on the wire to verify there was a high amp situation? The breaker could trip due to a few reasons like a dead short to ground in the compressor. Yeah ,that is a high amp condition but its only for a split second as compared to a sustained high amp that trips the breaker after a few minutes or so.

bill_105

Here's what happened

Long story short.My daughter started using a portable space heater, microwave,toaster oven and coffee maker all on a 20 amp circuit. It took them awhile figure out how to not trip the breaker. The place was fine for 14 years with what it was wired for.

It's a strange coincidence the freezer broke now Oh ya, they also put up some extension cords for light not for exterior use

SWEI

multi-wire branch circuits

A couple of things to watch out for on these.



On older houses, if someone has moved one of the wires to a different breaker (or moved one of the breakers to a different position in the panel) both can end up on the same phase, which doubles the current on the neutral.



On newer houses, code requires handle ties so that both breakers must be turned off in order to work on either circuit.  If one breaker trips, both must be turned off and then on to reset.  If the electrician installs a standard two-pole common-trip breaker, an overload on one circuit will trip both, which could cause issues (if something like a freezer is on the other leg.)

Ironman

In Another Recent Post

See my Explanation in this post:



http://www.heatinghelp.com/forum-thread/143971/Any-electricians-want-to-help-me-out-with-a-question