480V heating element control

Snap25

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I have a few tanks that each have 6 heating elements. I'm trying to figure out the best way to control them..

1, They each have a contactor in the control panel and I can gain better control of the temp by turning on/off individually as the tank temp deviates.

2, One contactor rated for all 6 elements combined.

3, Any other ideas?
 
Let's think this through before putting in an scr / triac.

the scr controls require that one leg of the system be on at all times.
I cannot say for sure about the triac.

in either case, you have a tank and when the power is turned off on a contactor, there is no leakage unless a contact welds.
with electronic controls such as the triac and scr, you can have current leakage.
if an scr or triac goes bad in the on position, how will you turn the power off?

We do NOT want any chance of electrical current in a tank getting to others.

I would recommend a mercury contactor rated higher than your contactor.
no contacts to weld or contactors to replace.

if I am wrong, someone please correct me.

james
 
Last edited:
James Mcquade said:
Let's think this through before putting in an scr / triac.

the scr controls require that one leg of the system be on at all times.
I cannot say for sure about the triac.

in either case, you have a tank and when the power is turned off on a contactor, there is no leakage unless a contact welds.
with electronic controls such as the triac and scr, you can have current leakage.
if an scr or triac goes bad in the on position, how will you turn the power off?

We do NOT want any chance of electrical current in a tank getting to others.

I would recommend a mercury contactor rated higher than your contactor.
no contacts to weld or contactors to replace.

if I am wrong, someone please correct me.

james
Click to expand...

You can get scr with 3phase control I believe. Either way, you would want a contractor ahead of the scr that is part of the enable/overtemp/safety circuit. All would need to be good to go to turn on the contractor that sends power into the scr.
 
g.mccormick said:
...you would want a contactor ahead of the scr that is part of the enable/overtemp/safety circuit. All would need to be good to go to turn on the contactor that sends power into the scr.
Click to expand...
+1 for contactor. It's a must.
The 3 pole Crydom is fine, but pricy. With three phase, you only need to control two of them. Two single phase SCRs would be fine, along with the contactor of course.

Edit: Size current rating of SSR at 3.5x the heater current. For the 25 Amp Crydom, the heaters should only draw a maximum of ~7 Amps per phase.
 
Last edited:
Are all 6 elements the same size?

If you want 0-100% power control you would only need SCR control on one of them the rest can be switched, or rather I should say that each of them has a contactor and one of them has an SCR after
 
So a contactor for all 6 and a SCR on one heating element (after the contactor)?

Toggle the other 5 heat elements at different deviation stages and use the SCR to maintain?
 
I would do 1 large contractor feeding 1 large scr feeding all of the elements. I would have fusing ahead of contractor for total load, and each element fused after the scr. This all assumes that the size of the elements makes this economical. If the elements are large, then it may make more economical.oval sense to split them into groups of two or three, each with contractor and scr.
 
Snap25 said:
I only have to control 2 out of the 3 legs? The other one is live going to the heating element?
Click to expand...

Yes that is one way that most 3phase scr work. You need the contractor ahead of the scr to completely remove all power from elements.
 

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