Electric baseboard heater question

Hi. We've got a couple of electric baseboard heaters that appear to be connected to a relay that apparently runs to a wall mounted thermostat. We're trying to track down a power problem. Service disconnect on the circuit box trips soon after baseboards start heating. No trouble when their breakers are turned off. Can anyone tell me what the symptoms of a faulty heater relay would be? Could it allow to much current to pass? Thank you!
KT
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_Service_ disconnect? Really? Takes out the whole house? Are you sure you don't mean branch circuit breaker? (probably a pair of breakers tied together).
If it's really the service disconnect, we need more detail. Ie: how big are the main breakers? What is the combined wattage of the heaters?
Do you have a whole-house ground fault detector?
I can't help thinking that you're really going to need an electrician for these.
If you have a whole-house ground fault detector, it's probably trying to tell you that one of the baseboards has a wireing fault (short to ground).
It could be that you're on a relatively small service, and that running the set of heaters all at once are too much for it. In which case you'll need to upgrade your service (or use something other than electric heat).

Unlikely to be the relay. Relays either "doesn't open" (won't stop heating), "doesn't close" (won't start heating) or makes the breaker go "bang" real fast (short). If the relay short is causing the main breaker to trip, you have big problems. If you're getting heat from the heaters, it's probably not the relay.
If it's the branch breakers:
Two main possibilities:
1) One of the baseboards is going bad and drawing too much current. 2) The breaker is "getting tired" and is tripping at too low a current.
If you could borrow an amprobe, that'd be the best way to test the current on each of the heaters.
--
Chris Lewis, Una confibula non set est
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snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote in message

It is actually the service disconnect, which is a 100 A breaker, and unfortunately does take out the whole house.

The heaters are on a sub-box (100A) off of a main box (also 100A). We have two electric baseboards (2500 Watts, 240V) controlled by two 20A breakers, a 'thermostat circuit' (24V 0.15 Amps/Line Voltage circuit 240 V AC Switched 25A), and a separate Honeywell thermostat. I'm not sure how it is all connected, but based on the label, I assume the thermostat circuit reduces the voltage before it hits the thermostat. The system has been in place for over 16 yrs with no prior problems.

I don't think so.

I know this is probably inevitable, we're just hoping to rule out a simpler problem with the heaters first.

We initially thought it was a load issue with recent heavy use of an electric dryer, portable electric heaters, baseboards, etc., but have been able to narrow it down so that we lose service only when the breakers to the baseboard heaters are on. Also, due to recent replacing of many appliances, our overall load should be less than in previous years in which we experienced no problems.

We do get heat from the heaters, and I guess what I am looking at may not be a relay. It is a small metal box near the fuse box labelled as a 'Thermostat Circuit (24V 0.15 Amps/Line Voltage circuit 240 V AC Switched 25A).' Does the same apply here?

That's what we're hoping, however, we still are wondering why, if it is heater related, wouldn't their own breakers not trip first, or if not, at least the the breaker controlling the sub-box that they're on, before tripping the main power?

Our second thought was that the main service disconnect breaker is faulty, but it seems odd that we only lose power after the heater breakers are on. We have tried reducing the load also with everything off except for heaters (and lights in one room) - but the main still trips within minutes. W/out the heater breakers on, the power stays on continually. We're going to try really loading up the system, without using the heaters, to see if the service can be tripped with a load outside of the heaters.

I'll see if I can get my hands on one. Someone more fluent than me in testing will be performing any tests. Is there a way to test the thermostat circuit box also?
We've got some things to try now, but would appreciate any added insight that you can offer. Thank you for your reply!
Katie
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Katie - the thermostat circuit is simple, it allows the use of a standard, low voltage thermostat to control one or more high voltage heater(s)
It does this through a relay or contactor which has a low voltage electromagnetic coil which "tells" a high-voltage switch what to do.
DO you know where the relay(s) are?
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Let's see if I can cut to the chase here:
You have a 100A main panel, with a 100A subpanel. The heaters are fed off the 100A subpanel (is the stove, dryer too?). The heaters are on two 20A 240V circuits. When the heaters turn on, the main (not subpanel) breaker (service disconnect) trips.
Points to consider:
1) "To code", the maximum current the heater circuits can draw in total is 32A (80% of 2x20). If it's more than 20A apiece the branch breakers should trip (but see below regarding massive shorts).
2) You have a low voltage thermostat circuit. This means: a small transformer converts 220V to 24V. The thermostat (you have only one thermostat, right?) acts as switch to control 24V to the relay. The coil on the relay is 24V. The contacts that the relay opens/closes are 240V driving the heaters. Most furnaces have low voltage or "millivolt" thermostat circuits - the relay is inside the furnace, transformer often mounted nearby. With electric heat, the relay has to switch a lot more current.
3) The thing circuit corresponding to the 'Thermostat Circuit (24V 0.15 Amps/Line Voltage circuit 240 V AC Switched 25A).' powers the transformer (at least). The small box you see is probably the transformer.
I'm not an electrician, and I've not worked with a low voltage thermostat system for electric heating since the mid 70's, so, I'm not quite sure of the current practise/hardware is. That "small device" could actually be both the transformer and relay (one thermostat: if there's two 220V circuits going into and out of it - total of four cables _plus_ smaller wires going to the thermostat. If there are two thermostats involved, there are likely two relays hidden somewhere).
Or, the relay is parked somewhere else. By code, the relay needs to be "accessible". But that may mean that it's in the wall behind something. [We installed ours in the wall cavity with the in-wall forced air heater. Access by unscrewing the heater from the wall.]
There's just about nothing the heaters do on their own that would trip a 100A breaker before their own 20A breakers. That goes for the relay[s], transformer[s] and thermostat[s] too.
I can think of two possibilities:
1) "tired" main breaker. But the stove and dryer simultaneously should be able to trip it. Probably not this.
2) One of the heaters has a temperature-induced short. Ie: when it heats up, a hot-ground short occurs and the main breaker simply trips faster than the 20A breaker on a massive short.
It's remotely possible this is the relay (or even the transformer connection), but I'd suspect a heater first. You should be able to smell ozone, or hear it go "bang", or find scorch marks in the device that's shorting out. Or all three. 100A+ shorts aren't subtle things. They usually make their presence known. The lights should dim momentarily when this happens for example.
If you find burnt contacts on the relay, be aware that they may be the _result_ of a heater problem. So you'll have to check the heaters out too.
You're really going to need an amprobe (and someone who knows how to use one) to diagnose this if you can't sniff out the problem directly.
Ie: is the main breaker really seeing >100A when it trips? Do any of the heater circuits spike >100A when the main goes?
For anything other than a solid diagnosis of a heater/relay/transformer going bad and spiking >100A, you'll need an electrician.
[Other highly remote possibilities: temperature-induced short _inside_ panel. Etc. This requires experience to diagnose.]
Be _careful_. 100A breakers tripping implies that there's a lot of energy going _somewhere_. Best not to be _you_. Don't be standing around touching the panel or heaters when this thing is likely to trip.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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sure
tied
"millivolt"
Can tell you right now, the thermostats will be line voltage and NOT 24VAC, but 220VAC...the rating on the stat is all he put up, and most line stats also have the 24VAC rating listed, simply because they can be used in a low voltage setup....I have not seen a baseboard heater that had a 24VAC transformer in it in so long...and the one we DID see had been rigged up that way.
The only relay, in a baseboard system like that, is the stat...its either on, or off...thats it.

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Cris, in many northern climates, especially where electricity is cheap and electric baseboard more common, many homes use a low-voltage stat and relay to control the electric heaters.
Reason being, there are no line voltage stats commonly available (Largest I've seen is rated 22a @ 240v) that can accomodate more than a couple of baseboards in the same large room, like a livingroom / diningroom / kitchen / foyer area.
Maybe in the Carolinas the footage of electric baseboards is is much lower, but up here it's often times wall to wall baseboard, an no line volt stat can control all that as a single zone.
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As described, the OP's system appears to have what is likely a 24V transformer on it. It also appears to be _two_ circuits fired off a single T-stat. And note the other posting about "great white north".
In the installation I did it had two 2000W baseboards and a 3000W fan heater on a single T-stat - two 240V circuits. The building had approximately 12Kw of electric heat in total (200A service).
I assure you, that one T-stat didn't pass 240V ~35A. It was one of those itsy-bitsy round (chromolox if you remember that far back) with a teeny-weenie mercury switch (that could probably safely pass all of about an amp or two) connected to the relay with 18ga wire.
AFAIK the relay isn't usually inside the baseboards. The relays go somewhere else (ie: the panel or some other accessible place) to control multiple large loads at once. In ours, the relay went in the cavity behind the wall heater, and controlled two 240V circuits.
Please try to trim followups. I know I write good ;-), but wading through pages of my own posting to find a few lines of response is a bit of a PITA.
--
Chris Lewis, Una confibula non set est
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Hi all,
I'm new here and need some basic info - We've got two electric baseboards (2500 Watts, 240V) controlled by two 20A breakers, a 'thermostat circuit' (24V 0.15 Amps/Line Voltage circuit 240 V AC Switched 25A), and a separate Honeywell thermostat. The system has been in place for over 16 yrs. Just recently, we started losing power (main 100A service disconnect gets tripped.) We initially thought it was a load issue with recent heavy use of an electric dryer, portable electric heaters, baseboards, etc., but have been able to narrow it down so that we lose service only when the breakers to the baseboard heaters are on. These are on a sub-box (100A) off of a main box (100A, I think). I'm not sure how the baseboards are wired, but shouldn't they trip their own breakers (or even the breaker on the main for the sub-box) before tripping the main service? Can you tell me what the symptoms of a faulty 'thermostat circuit' box would be? Any way to test this? Our second thought is that the main service disconnect breaker is faulty, but it seems odd that we only lose power after the heater breakers are on. We have tried this also with everything off except for heaters (and lights in one room) - but the main still trips. Can you shed some light on any of this, mainly what a faulty thermostat circuit would do? Don't worry - someone more knowledgable than myself will be carrying out any tests! Thank you!
Katie
Sorry if a similar message shows up twice - I posted yesterday, but haven't seen it come up yet.
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Sometimes, a dead short circuit can cause a backstream overcurrent protection device to open, rather than the individual specific circuit breaker.
I suspect faulty wiring either inside one of the baseboard heaters, or their associated circuits somewhere between the panel and the actual baseboard heaters themselves.
If one heater is butted against the other, and the second heater fed through the first, I'd look into the wires that run through the "first" baseboard to see if they're defective - possible an electrician used wire that was handy instead of wire that could withstand the heat.
Second place I'd look is the connector that the cable which feeds each heater is connected to - the mechanical clamp where the wire comes out of the wall and into the heater. Make sure it's not pinching through the wires.
Third - have you done any nailing lately? Hung any pictures, drilled any walls, nailed any new mouldings around your walls/floors?
I'd also have a look at the circuit breaker which SHOULD be opening upon a short circuit, and the one that is opening instead and replace them. Breakers are cheap and every once in a while you get a precarious one.
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