Expert: Dan Griffin - 5/18/2009

Question
I have an ice cream truck with two freezers. I connected a three-headed extension cord to another extension cord and then plugged it into the outside outlet. After a week, my freezers shut off because the breaker switched tripped. Needless to say I lost a lot of ice cream. To prevent this I bought a 13 amp extension cord and plugged each freezer into it's own ex. cord then ran the cords into the house (same outlet). What I want to know is if this will trip the breaker again if it's on the same outlet. I looked on the back of one freezer and it says 5 amps. I haven't checked the other one yet. I'm not sure what the amps are on the outlet. It's just a basic room outlet. I don't want my freezers to shut off again and I also don't want to cause a fire. This is my boyfriends house and let's just say he would no longer be my boyfriend if this happened. Does it matter what the amps are on the extension cord? If the amps are lower on the freezer than the extension cord and the outlet am I good? A guy at Lowes told me that the amps on the extension cord should be the same as the outlet. Is there a solution where I won't have to worry about it catching fire or shutting off again? What I'd like to do is up the amps on the back deck outlet because the outlets I'm using now have to be fed through the front windows and I'm not liking that too well because it's on the first floor. Any suggestions would be helpful. Many thanks!

Answer
Cheryl, here a few facts.  Residential receptacles are selfom on their own circuit, they usually share the circuit with several receptacles.  The total load on the circuit is what determines the breaker tripping.  If the wires are getting too hot, the breaker trips.  This can be caused by too many things on the same circuit or small cords trying to deliver too many amps.  Most residential receptacle circuits are 15 amp circuit breakers (you can look in the breaker panel and see the number on the end of the breaker) which can be fed with either #12 or #14 wire.  #14 is smaller than 12.  YOu should be able to kill the breaker  that feeds the receptacle you are trying to use and check all lights and receptacles to see what others are on the same circuit.  Let's assume for a moment that you have 3 freezers that each draw 5 amps and that they are all running at the same time - you will be drawing 15 amps.  Motor and compressor loads draw more current at start up than when they are running.  YOu are using all the amps that one circuit can supply and if they cycle off and restart they will draw more and can well trip the breaker again.

Cords are rated based on the gauge of the wire and the length of the cord.  If your cords are 12 gauge and the length doesn't get too long they can deliver the power.  As the cord gets too long you can suffer voltage drop.  If you have all 3 cords plugged into one receptacle you certainly are flirting with blowing a breaker again.  If there is a way to get the cords on different circuits you do decrease the possibility.

I'm sure the salesman meant to say if the gauge of the extension cord was as large or larger than the house wiring you should be all right (the bigger the number, the smaller the wire size).  The real issue is the wattage being consumed and the amp load that will be drawn at start up.  If the usage exceeds the ampacity of the circuit it is designed to trip to protect the house wiring.

I really can't see the set up, but if you have a way to plug into different circuits that aren't already full, you will be better off.