New electric baseboard stopped working - troubleshooting

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Old 11-22-15, 05:03 PM
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New electric baseboard stopped working - troubleshooting

Hi all,

One of my electric baseboards stopped working and I'm not sure what troubleshooting step to try next. I'm a bit stumped.

The whole house is heated via electric baseboards. Last Winter/Spring, a professional renovation was done where two walls were removed to create a common area kitchen, dinning, living room.

Where there used to be two thermostats for two 8' baseboards, there is now just one thermostat for two identical, new 8' baseboards (Ouellet brand). The master electrician said there is no single thermostat that could handle the power of these two baseboards, so he installed a 110V thermostat that drives a pair of RIBU2C devices/relays (link).

This worked nicely and quietly through Spring, maybe 6 weeks. The heat wasn't used during the Summer, and now this Fall one of the two baseboards is no longer heating up. I'm sure no electrical work has taken place since, and I don't recall the impaired baseboard being banged. It certainly sports no mark indicating damage. So I did a little troubleshooting.

When the thermostat calls for heat, there is indeed 220V at the cold baseboard. After shutting off the breaker and disconnecting the baseboard, I measured the heating element resistance and it registered 30 Ohms, which is exactly the same that I got from the working baseboard, and which seems to make sense for a 4000W board (11.5A squared times 30 Ohms = 4000W).

I think there is a high temp limit switch in them baseboards. Looks like a black plastic think hooked up to a bare copper wire that runs a couple of inches above the heating element. That switch measured zero Ohm (ie closed) which I would expect.

From the above, I deduce that the baseboard that won't heat appears otherwise healthy.

In my attic there is a large junction box containing the pair of RIBU2C's. When there is a call for heat, one LED per RIBU2C lights up, but it doesn't stay on steady. I didn't measure exactly, but it's like 12 seconds on, 5 seconds off, repeat. I have no idea if that is expected, but I'll guess yes since it works for one of the baseboards.

So, if the thermostat is working, the cold baseboard is showing no fault, and the relays are behaving the same way, what the deuce could it be? How was my baseboard troubleshooting procedure wrong? What am I assuming about the relay that may not be true.

Thanks in advance,
JP
 
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Old 11-22-15, 05:18 PM
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Did you check for 240vac ON the baseboard element..... not just the incoming wiring ?
There is usually a safety/overheat stat in those heaters. It usually connects one of the supply wires to the far end of the heating element.

Those RIB relays are only spec'ed for 10A (2400w) resistive use and the red LED's should not blink.
 
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Old 11-22-15, 05:20 PM
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The 110 thermostat doesn't sound right. I've only installed electric baseboards once. There were two of them & one thermostat controlled & still controls both heaters. On the first link that you posted, there is a list of thermostats. The Series OTH2750 is rated at 240V. I don't know why the "master electrician" said that one thermostat couldn't control two both heaters.
 
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Old 11-22-15, 05:24 PM
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The electrician is correct and he should be using a single 120v thermostat to control the two RIB's.
 
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Old 11-22-15, 05:50 PM
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Pete got me thinking (it hurt a little but I got over it ) about overloading the relays and I rechecked the current need. I was off a little bit.

Per the manufacturer, each baseboard only consumes 8.34A
[ATTACH=CONFIG]59210[/ATTACH]

I'll take another crack at validating the voltage at the element, making sure to measure with and without the temp switch.

I'm not sure what to make of the relays cycling. I'll see if the thermostat is set for the right kind of "furnace". Regardless, that wouldn't explain why one heating element is working and not the other.

Any chance a relay is busted in a way where it provides a voltage but cannot somehow furnish the required current? I'm not sure I'm brave enough to attempt to measure the current by inlining my multi-meter.
 
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Old 11-22-15, 06:06 PM
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No.... you do NOT want to put your meter in series to check amperage.

If the voltage is there...... the heater would work.
Those are 2kw heaters.
 
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Old 11-22-15, 06:07 PM
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Did you measure the 240 vac at the same location that you measured the 30 ohms? If not. there could be a disconnect between the 2 measuring points. Also, the data sheet for the relay says the contacts are rated for 10A. The contacts will fail prematurely if they are switching 11.5A.
The data sheet provides no information on how the LED is powered except to say the LED is ON when the relay is energized. My guess is it may be a bad solder joint. How is the LED on the other relay module when the t'sat call for heat?
Good luck.
 
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Old 11-23-15, 08:51 PM
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Mystery solved. I opened up the giant j-box that contains the 2 RIBU2C and spent quality time studying the mess of wires: 2 relays at 8 wires each plus 8 NM-2. Phew.

Turns out one relay had only 3 wires connected. The missing one was power to the cold baseboard. Hooked that up and voila.

I did make one mistake in troubleshooting and measuring voltage. I had assumed that if I measured 120V at two points it was equivalent to 240V total (said simply). But I forgot that at 240V there is no neutral, so even when one leg is switched off, the other leg will cause 120V to be present. Lesson learned.

Thanks for all the ideas and feedback.
 
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Old 11-23-15, 09:01 PM
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But I forgot that at 240V there is no neutral, so even when one leg is switched off, the other leg will cause 120V to be present.
That is an important thing to understand. Most people don't.

Glad you're in the heat there.
 
 

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