View Full Version : Tranformer overload?

04-04-2007, 06:55 PM
I have a confusing situation. I installed a bunch of lights, maxing out a cast 1200 Master series transformer and I am tripping breakers at a gfci outlet and one in the house. No breakers on the transformer are popping but the house breaker worries me. I checked the amps and am under the limit on each common and at 9 amps on the primary. Aside from the fact that I am pushing this thing close to its limit, is there any other obvious reason that might cause this?

04-04-2007, 07:43 PM
Is the outlet that the transformer is plugged into on it's own dedicated circuit? If not, you could be overloading.

04-04-2007, 08:23 PM
The gfci outlet was dedicated on a 20 amp breaker. It is a jandy pool control box ( pumps and filters not yet active), and I mounted the transformer next to it. The second time, I used about 80 feet of extension cord and flicked the lights 3 or 4 times and the house breaker blew. Homeowner was not there to see what the breaker was but will look later tonight when I go adjust some things.

04-04-2007, 08:26 PM
How long is it on before it trips?

04-04-2007, 09:47 PM
It will work fine the first couple of times and trip immediately when I turn on the switch the fouth time or so. I was only leaving it on for 10-20 secs and then off and back on quickly.

04-04-2007, 10:31 PM
Lots of things I am a line electrician I am not however we had a dedicated GFI for our pond that would trip which seemed randomly. Finally found a short in the circuit.

when you said you have it maxed out....are you running the full 1,200 advertised or at you 80% of 1,200?

What is the max watts running on one run? and 9 amps is your high?

04-04-2007, 11:11 PM
I think I worked it out. The house breaker was not dedicated so something may have been running. After reading through these forums I added an extension cord tonight to the dedicated gfci on the jandy box and everything is fine. Inrush? 9 amps was the primary on the little loop on the cast transformer. But I had 19 on one common and 16 on another... Nothing higher than the specs called for with all the lights running.

04-04-2007, 11:18 PM
OK, so you didn't have a dedicated circuit. This is something that a lot of guys don't check. It's very important to know everything that is on a circuit that you are using for your lighting. You can only load a 20 amp circuit to 16 amps. If you are pulling 9 amps on the circuit, you are only leaving 7 amps for everything else on the circuit. If at all possible, have a separate, dedicated circuit for your lighting.

I'm glad you figured it out, now what are you going to do to get the needed power to your transformer?

04-04-2007, 11:32 PM
Well since the dedicated circuit is the one only a few feet from the transformer, I am going to try to get a longer cord for the transformer or have the electrician install a different type of breaker. Ill let you know which we do. I initally hooked it up to the dedicated line but I guess that breaker is the weird type. Thanks for all the responses. It is great to find a community of people helping each other out like this.

Mike & Lucia
04-04-2007, 11:42 PM
Muy Loco,
You've identified your problem is on the primary side. Get an electrician to help get you the power you need. As for the Cast tranny, you're fine at 19A on the common. Hell, I load 'em to 22 if I have balanced loads. Put your concerns aside - if it was too much, you would trip the secondary. And 9 amps on the monster is pushing the limit, but that's not going to trip it either. A 1200 has an advertised max of 10A on the primary breaker, but there is actually some head room there too. Cast doesn't advertise the true rating of the internal breaker. Your problemo is definitely on the branch feeding your outlet. Get a dedicated circuit.

BTW - I gave up those monsters two years ago, I got tired of wrestling the boxes, and trying to get all those wires into one box. I would have used two 600's (or a 600 and a 900, in this case) and started them up a minute apart from each other. My $.02


mr mow
04-04-2007, 11:56 PM
watch your wire gauge size as well-voltage drop-im sure you know. im a residential/commercial electrician,my fulltime. Dedicated was my guess as well and or an extension cord but was beaten to the punch. Dont anything about the transformer other than the numbers,dont do outdoor lighting,but every electrician thats in the lawn care trade should its right up their alley.

04-05-2007, 05:22 PM
I am still a little confused but I can tell you this- the Jandy systems dedicated GFCI is VERY FINICKY. I can tell you that they are usually run through the pool lights or something else in the panel and they always trip very easily.

A really cool upsell for lighting is the Jandy system itself. You can run the lights through one of the aux inputs in the panel and then the homeowner can control the lighting from inside the house.You have to get one of the modules from a pool supply place . Unless you have 120 volt experience do not try this on your own.


Firefly Lighting
04-05-2007, 06:25 PM
Is the outlet that you are plugging the transformer into the one on the side of the Jandy panel? If so and for future info for the rest of you, that outlet is not there to be plugged into, it is there as the gfi for the pool lights and will always be a problem if you try and plug into it. Solution- Pull a different dedicated circuit from the Jandy panel.

04-06-2007, 09:11 AM
Thanks for all the info. I might try the two trannie idea on the next job. In the meantime, the electrician installed a different breaker on the dedicated circuit and all is good now.