SuperlecDirect - ElectriciansForums.net Electrical Suppliers
This official sponsor may provide discounts for members

Discuss Timer and local thermostat control of 3 x heaters on 3 phases. Wiring logic help please! in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

I'm fitting oil-filled panel heating into two rooms of a remote workshop, with (currently) a 20A x three phase supply.

Control, for occasional use only, is needed as follows:
1. A wall-mounted and easily-adjustable mechanical timer to set all the heating to come on an hour or two before people arrive.
2. Room thermostats to control temp in each room individually. Room 1 has one wall thermostat and one heater; room two has one wall thermostat and two heaters.

Due to supply limitations each heater must be on a different phase.

The block sketch below was knocked out by me over breakfast. I am not proud of the graphical standard :)

I'm unhappy with the second SP contactor. It feels clunky, over-complicated and ill-designed. I could of course fit a second thermostat in Room 2, simplifying the logic and deleting the second contactor, but that's even worse.

As always in life: Is there a better way of doing it? :)

Heaters.jpg

ps. Can anyone recommend a model of oil-filled radiator which does not have any local room thermostat or complicated controls, designed specifically for central control. Difficult to find!
It has to be oil-filled with no exposed elements or blown/convected hot air, as explosives are handled in these rooms and it's the only type allowed.
 
Last edited:
Aico Carbon Monoxide Detectors
This official sponsor may provide discounts for members
  • Thread Starter Thread Starter
  • #3
Don't most oil filled rads have stats on them.
Yes, but they are useless things which aren't accurate, are often complicated, and you need to visit each heater to see what it's set to.
A single wall stat per room is much more obvious to everyone how it works, is easy to set, and you can be sure the room is off simply by tuning it all the way down.
 
Room 2 I would switch both by way of the contactor. The only issue I see are the stats and a contactor in a possible explosive atmosphere. Do they not have a heating boiler.
 
Last edited:
Many of this type of area I have seen the heater is outside the room. Normally a space heater vented into it with dampers fitted.
 
  • Thread Starter Thread Starter
  • #9
Room 2 I would switch both by way of the contactor. ...
You mean use a 2 or more pole contactor, for consistency? Can't be on the same single pole contactor as the two heaters must be on different phases.
... The only issue I see are the stats and a contactor in a possible explosive atmosphere. Do they not have a heating boiler. ... Many of this type of area I have seen the heater is outside the room. Normally a space heater vented into it with dampers fitted.
... Perhaps a call to these people for advice on suitable electric heaters for a hazardous area ...
A digression, but there is NO explosive atmosphere hazard!
Many times I have needed to explain this difference to regulators. The electrical regs are concerned with intrinsically safe fittings for use in potentially explosives atmospheres, which are entirely absent from most explosives processing/demonstration/teaching areas as in this installation.
The regs you refer to are aimed at flammable gases, volatile flammable liquids, or flammable powders which might become airborne.
When all that is present is bulk plastic explosives or enclosed ammunition, these cannot possibly give rise to an explosive atmosphere. All one needs to watch out for is hot surfaces and fire, so anything radiant, or convector heating with exposed elements, is out. A dodgy switch or relay can spark away in its box and nothing will happen :)

ps. These are remote sheds in a field. There is no oil heating. So it has to be electric.
 
Last edited:
All clear now. You can run two phases through a four-pole contactor, two lines and their neutrals. Using a four-pole gives termination points for the neutrals and supply it using a four core cable.
 
  • Thread Starter Thread Starter
  • #11
Thanks, gentlemen, for the comments so far.
Unless someone comes up with a better way of wiring this, without the multiple contactors, I think I'll fit two wall thermostats in Room 2, one for each heater. It's the simplest, most logical way.
I suppose I can justify that by it providing the ability to leave only one heater on very low, limiting any background anti-frost load in Room 2 to only 1.5kW.
 
Due to LOT20 requirements you may struggle to find any panel heaters that don’t have a thermostat of some sort integrated.

used to use Nobo heaters but even these now need the control module fitted even though we are controlling them separately.

if you find something let me know as I need half a dozen for an office project.

Paul
 
  • Thread Starter Thread Starter
  • #13
Due to LOT20 requirements you may struggle to find any panel heaters that don’t have a thermostat of some sort integrated.
used to use Nobo heaters but even these now need the control module fitted even though we are controlling them separately. ...
Thanks Paul. Maybe they don't exist any more. I'm going to one these from EBay to experiment with:

Capture.JPG

At least they have only what looks like a very simple thermostat which can either be taken apart and shorted out, or left on max.
A lot of the models I found have complex electronic timers and stats, which I don't trust to default to max on after power interruptions.
 
I would fit some standard rads but manufacture some guards to prevent unauthorized regulation.
 
  • Thread Starter Thread Starter
  • #15
I would fit some standard rads but manufacture some guards to prevent unauthorized regulation.
Yup, agreed. Or get the epoxy glue out! :)
Post automatically merged:

Due to LOT20 requirements you may struggle ...
I'd never heard of LOT20 so just looked it up. It explains everything.
What load of bol-ocks: now any wall-mounted heater must have complex timers, open-window sensors and so on, whether it's standalone (which is sensible), or part of a centrally-controlled system (a total nuisance, and daft).
Time for a bit of reverse engineering.
 
Tubular heaters are another option, you may need to install more of them but they have no stats or adjustments fitted.
 
  • Thread Starter Thread Starter
  • #17
Tubular heaters are another option, you may need to install more of them but they have no stats or adjustments fitted.
Good idea!
I did a bit of research, but the max power I can find is 360W, so it would need banks of four, and the price adds up. And they are six feet long, so a bit unwieldy. Would have been ideal for smaller rooms.
Capture.JPG
 

Lucien Nunes

-
Mentor
Arms
Esteemed
An alternative, depending on the cable runs involved, would be to put three DP contactors next to the DB, one per heater, each fed from an SP MCB and feeding the heater connection unit. Fit one stat in each room wired back in 1.0mm² to the contactor box. Feed the timer from a 6A control MCB either in the board or the contactor box, then take its output to both stats and the returns from the stat to the appropriate contactors. Advantages include not switching the heater load with the stats so they should last longer, and simplicity; three identical single-phase power circuits and one single-phase control circuit.
 
If your going from room stats in each room wouldn't three separate single phase with a control loop back from the box. Also if there single phase heater would a 3 phase breaker be the best idea rather than a three single phase breakers.
 

GBDamo

-
Supporter
What is your budget here?

Could a local three phase boiler and wet system not fulfill the brief? May need a buffer tank.

Might suit the environment better.
 
  • Thread Starter Thread Starter
  • #21
An alternative, depending on the cable runs involved, would be to put three DP contactors next to the DB, one per heater, each fed from an SP MCB and feeding the heater connection unit. Fit one stat in each room wired back in 1.0mm² to the contactor box. Feed the timer from a 6A control MCB either in the board or the contactor box, then take its output to both stats and the returns from the stat to the appropriate contactors. Advantages include not switching the heater load with the stats so they should last longer, and simplicity; three identical single-phase power circuits and one single-phase control circuit.
This I like, thank you for taking the time to think about it.

I agree yours is a more elegant system, but I wanted to avoid the complication and possible future confusion of feeding stat control lines back to the DB area. The runs are not easy.

I certainly agree about causing the stats to last longer - I like using relays for all kinds of things, and personally never use 13A stats direct wired on anything over about 6A, which this is, just!

I was using a 3P MCB only because there's a 4-pole contactor, and I like reducing component count. The 10A 3P MCB would simply be labelled 'Heating'.

Bloody hell this is a difficult call :) and I need to order parts and finish it by Thursday.

Here's a compromise I alluded to earlier: Keep the 3P MCB and one timer-circuit-controlled 4-pole contactor, which can be inside the DB so no external box is needed. Feed to three quality 13A stats, direct wired to the 6A heaters.

Do you think that under-run electronic stats with internal encapsulated relays are any less reliable than contactors? I agree that the old bi-metal type are trash, run hot and burn out, but those days are over. Aren't they? :)
 

Reply to Timer and local thermostat control of 3 x heaters on 3 phases. Wiring logic help please! in the Electrical Forum area at ElectriciansForums.net

CK Tools :) The professionals choice when it comes to Electrical Tools
This official sponsor may provide discounts for members

Select the ways in which you gain online business

  • MyBuilder.com

  • Federation of Master Builders

  • CheckaTrade.com

  • RatedPeople.com

  • TrustaTrader.com

  • Which? (TrustedTraders.Which.co.uk)

  • MyJobQuote.co.uk

  • Yell.com

  • Google Paid Advertising

  • Own Website with Natural Ranking (SEO'd website)

  • Social Media (Facebook Twitter Instagram etc)

  • Word of Mouth Only for me


Results are only viewable after voting.

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
Aico 3000 Range
This official sponsor may provide discounts for members
Top Bottom