(01-24-2019, 12:50 PM)®smpr_fi_mac® Wrote: My mistake. It's actually rated at 7500 watts. I'll get a picture of it and specs later today.
Yeah, simply using the thermostat on it is the easiest and cheapest route, but as it calls for a required mounting height of 8', that kinda makes operating the thermostat dial a PITA.
It's a ceiling mount unit, with a U bracket that gets bolted to a stud in the ceiling. With a 12' ceiling, I'll instead fab a bracket out of dimensioned lumber to hang it from the wall.
Who knows. I may just put a heavy duty switch inline and use that to turn it on and off.
By the time I figure out what I'll do it'll likely be spring!
Post a picture of the schematic and TDKP or I can tell you if you need a line voltage thermostat. The units at work had a 24 vac transformer and contactor built in but could be wired with either the built in thermostat of a common external furnace type thermostat. Roly
(01-24-2019, 12:50 PM)®smpr_fi_mac® Wrote: My mistake. It's actually rated at 7500 watts. I'll get a picture of it and specs later today.
<snip>
It's a ceiling mount unit, with a U bracket that gets bolted to a stud in the ceiling.
That changes things. The 7.5kW unit from Northern Tool has a junction block to add an external thermostat. It's possible your unit does, too.
(01-24-2019, 04:36 PM)Roly Wrote: Post a picture of the schematic and TDKP or I can tell you if you need a line voltage thermostat. The units at work had a 24 vac transformer and contactor built in but could be wired with either the built in thermostat of a common external furnace type thermostat. Roly
Good call! Figure 9 in the manual for that unit* shows the remote thermostat terminal block. Line voltage, but small current.
01-24-2019, 08:15 PM (This post was last modified: 01-24-2019, 08:16 PM by pprobus.)
(01-24-2019, 01:07 PM)TDKPE Wrote: That load is mainly resistive (as opposed to inductive), so a very long wiring run with large voltage drop will result in the heater actually allowing a lower current in the wiring and breakers. Total resistance is higher, so total current is lower, for the same source voltage.
Sounds like the thermostat simply let go. Time for a heavy line-voltage relay and better thermostat.
That's pretty much what I figured on doing. My heater does have a fan, so it would need to pull more amps with the longer run, did not really think about the resistive heating load pulling less than the 20.x amps. I need to get a clamp meter and check out what's really going on.
Paul
Paul
They were right, I SHOULDN'T have tried it at home!
01-25-2019, 08:35 AM (This post was last modified: 01-25-2019, 08:38 AM by TDKPE.)
I don't know why they're spec'ing a 45A overcurrent protection for a 31.25A device, wired for 39A (125%). It's not like it has a large induction motor that needs to start - that is most likely a small shaded-pole motor, which draws almost the same current at a stall as when it's at speed.
Be sure your thermostat wiring is 240V rated, too. Not 150V, low current 'thermostat wire'. I'd be inclined to use 14 gauge stranded in conduit with a length of flex to the unit.
There's also no overcurrent protection for small thermostat wires. Perhaps it's in the relay unit, though one end is direct to the mains power. Or there is none at all. Can't tell.
Any single-pole, 240V rated thermostat will suffice. They make cheap mechanical types, like my baseboard heater has, or better (maybe) electronic types that are line voltage rated.
Tom
“This place smells like that odd combination of flop sweat, hopelessness, aaaand feet"
(01-25-2019, 08:35 AM)TDKPE Wrote: I don't know why they're spec'ing a 45A overcurrent protection for a 31.25A device, wired for 39A (125%). It's not like it has a large induction motor that needs to start - that is most likely a small shaded-pole motor, which draws almost the same current at a stall as when it's at speed.
Be sure your thermostat wiring is 240V rated, too. Not 150V, low current 'thermostat wire'. I'd be inclined to use 14 gauge stranded in conduit with a length of flex to the unit.
There's also no overcurrent protection for small thermostat wires. Perhaps it's in the relay unit, though one end is direct to the mains power. Or there is none at all. Can't tell.
Any single-pole, 240V rated thermostat will suffice. They make cheap mechanical types, like my baseboard heater has, or better (maybe) electronic types that are line voltage rated.
Good catch on the voltage rating of thermostat wire, some are 150v and others 300v. I also thought it was strange that there was no overcurrent protection for the 16 ga thermostat wire since it is external of the heater. If you use the electronic type, check what wiring is needed, may need a neutral. Roly
01-25-2019, 10:48 AM (This post was last modified: 01-25-2019, 10:49 AM by TDKPE.)
(01-25-2019, 10:40 AM)®smpr_fi_mac® Wrote: This one looks good, aside from not meeting the wattage rating.
Why does that matter?
That one looks ok. You don't need 4-wire (opens both poles of a 240V load), but you could wire it using only one set of contacts. They also make 2-wire versions.
The wattage rating is basically irrelevant, as it's only controlling a relay, which takes a fraction of an ampere, especially at 240V.
Tom
“This place smells like that odd combination of flop sweat, hopelessness, aaaand feet"
Here are some supplies and tools we find essential in our everyday work around the shop. We may receive a commission from sales referred by our links; however, we have carefully selected these products for their usefulness and quality.
Time for a heavy line-voltage relay and better thermostat.