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Electrical Wiring in the Home/Residential, electric hot water heater with a countdown switch and DPC.


box at the heater
box at the heater  
Hi Bob,
Residential, electric hot water heater with a countdown switch and DPC.

I installed a Definite Purpose Connector (Square D = 8910DP32V02) to my electric hot water heater (residential) and control it with a countdown switch (Intermatic E1210W 120v 15amp). It ran for about 7 minutes and stopped. I canít figure out why.

The countdown switch has 4 wires; green, white and ground (ground running from the water heater box to the countdown switch) are wired together. Black on black-to the water heater box and red on white-to the water heater box.

The countdown switch, from the power supply Ė breaker side of the contactor Ė black wire to a 15 amp fuse (Fuse Holder, 15a, 250v and Fuse, 15A, MDA, 250VAC, PK 5) ĖĖ to the black wire coming from the countdown. The white wire from the countdown connected to the switch side of the connector. The opposite side of the connector white wire connected on the switch side of connector to the white side of the connector from the breaker.
I tied all the grounds together.

The water heater box, from the breaker white on left (upper right of the DPC in the picture) and black on right on the connector. Water heater same, but on opposite side of the contactor, white and black connected across from the breaker wires.

I have power going through the fuse so I ruled that out. I donít know how to test the switch because it gets its power from the controller and I donít know how to test the controller.

Like I said, it ran for about 7 minutes then stopped. The water in the heater is not up to temperature. When I went to the box I thought I could smell electricity, not burning but something. I thought it would be electricity running through new parts.

If I did the attachment correctly, it should be a picture of the box at the water heater. Top left is the breaker, bottom left the countdown switch, bottom right is the water heater, and on the bottom left in the back is the bussman fuse.

So where Iím at thinking wise, do I have a faulty countdown switch, faulty DPC, did I wire it incorrectly, did I wire it incorrectly and burn something out?

Thank you Bob,


You fried the timer by imposing 240 volts through the "coil" of the "contactor" to the timer which can only take 120 volts. In other words the black wire to the timer is off the fuse which is tapped to the incoming black "Line" wire from the panel. Then the white wire to the timer is connected in "series" through the "coil" of the contactor which is how it picks up 240 volts from the white "line" wire from the panel. Its easier to see if you put it on paper but thats what happened.

You need two things to make this work:

1.) a 2 pole 30 amp contactor with a 120 volt coil

2.) a separate source of 120 volt power for the timer and the contactor

Reason being the circuit for the water heater is straight 240 volts. No neutral (white) wire is present so you can get 120 volts for the timer and the coil.

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Licensed Master Electrician (32 years) 6165B Contractor in Closter New Jersey with 40 years total experience in Residential - Commercial - Industrial work. Emergency Service - General trouble shooting and repair work - ONAN & GENERAC generator installation - Paddle fans - Kitchen & Bath exhaust fans - AC lines - Smoke detectors - Telephone lines - Cable TV lines - Computer network cabling - Exterior lighting - Recessed lighting - Security lighting - (200 - 150 - 100 amp service up grades) - Electric Heat - New circuits - New appliance hook ups - and more ! FREE ESTIMATES 201-358-1552 Fully Insured


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"The Frank Williams School of Electrical Construction". My dear old boss is 100 ! and still going God Bless him. I started working for "Tenafly Electric" right out of high school at 19. He was tough but I learned more working for him in 8 and half years than most guys. We did mostly industrial work while doing some commercial and residential so I was fortunate to be exposed to all 3 areas of electrical construction. The guys I worked with were all good guys and I stay in touch with some of them still. Most of us went into our own buisness's which says something about the caliber of the guys I worked with. We had some interesting clients : Wella Corp. of shampoo fame, Farah Fawcett etc, I didn't buy shampoo for 10 years. It was a great place to work. Pan Am the former airline just before they went under, another great place to work, nice clean environment. C&C Metals, the largest button manufacturer in the US at that time, a not so clean environment but a very interesting place to work, lots of machine's cranking out buttons of all kinds but you had to be on your toes, it was a potentially dangerous place to be . All kinds of action going on around you.

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