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Discuss One way 240v flow HOW in the Electrical Forum area at ElectriciansForums.net

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Good Morning.

I have a fused spur which has 2x240v inputs and 1x240v out put.

The 240v inputs are from heating control panels. One is from a timer clock for hot water and the other from a large 1000l hoh water storage tank. The ouput is to the oil burner.

So the question is when i have i have a single input switched on with other input off the off input is getting a live feed, from the on input. Is there anything that can be wired in to make the flow one way only.

Thanks
 
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snowhead

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Mentor
The way to stop backfeeding , which is what you appear to describe, is to use a relay on each input.

What is the effect of the backfeed, both appear to be connected with Hot water, the issue is normally between Hot water and Heating?
 
  • Thread Starter Thread Starter
  • #3
Hi.

Thank you for the prompt response.

The backfeed means that the hotwater pump is constantly on. I have that circuit on the clocks, so effectively its ignored as the temp control of the storage tank is backfeeding it when it is maintaining the heat.

What type of relay is best to put on the inputs.

Thanks
 

Lucien Nunes

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Mentor
Arms
Esteemed
I have a fused spur which has 2x240v inputs and 1x240v out put
Is this a commercially made device, or are you saying there are two separate feeds connected to the input of one ordinary fused spur unit? (Which is obviously not a standard thing to do, and if the two sources are separate circuits it is highly dangerous as the isolation and OCPD is rendered inoperative)

The solution as mentioned above is to use two relays. Each relay's coil is controlled by one of the existing supplies. The spur box gets a new permanent feed, then its output goes through the two relay N/O contacts in parallel to the burner.

The relays need to have 230V coils and contacts rated for the load current of the burner.
Here's a completely random example:
16A 230V DPST DIN rail relay
 
The problem I have found with conventional relays is the noise they make when operating, I tend to use electronic relays instead, sorry don't have a random example.
 
  • Thread Starter Thread Starter
  • #6
Hi.

Attached is a basic diagram of the setup. In order to stop the back feed I have an isolation switch on the feed so that when I only want hot water I can turn off the hot storage control and just use the isolator. Its not ideal.

If I were 1584717072902420813428320832177.jpgto install the two relays, would they simply be wired into the circuits as per the second pic

Thanks
 
Last edited by a moderator:
  • Thread Starter Thread Starter
  • #7
Just checker the system. If the hot tank is not calling and the water circuit kicks in its not drawning any hot water as the pump on the boiler is not activating as the hot water circuit has no power due to the isolator. So need the relays.

I recently changed to oil from a wood pellet boiler which had two control inputs with zeroo volts. So this is the nightmare. Errrr
Post automatically merged:

What if i went back to a zero volt trigger? Is there a easier solution there.?
 
Is there any particular reason why this system couldn't be plumbed and wired using 2 port zone valves? These effectively act as relays, but the coil in the relay is replaced by the syncron motor in the valve. This has the added benefit that the boiler and pump won't receive a fire signal until it is physically proven that the hydraulic circuit is open, so prevents boiler lockout on overtemp.
 
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  • #10
Its has a two port value system on the hot water side. I have wired it to the call feed, but the back feed from the hot storage controller is causing the issue. Should i try to wire it back to the value in some way, or would i have the same back feed issue

Thanks
 
If you were to add a 2 port valve to the heating side as well, and wire as typical S Plan, you'd achieve the separation you require. That would be my approach unless there is a specific reason why that can't be done.
 
  • Thread Starter Thread Starter
  • #12
Hi

The hesting side i.e does have a 2 port value. Only the repol tlr2 control to regulate the temp in the storage tank. The tlr2 controller has a bridged 240v feed within the call for heat when required. As far as i can tell there is no back feed issue here, if the hot water circuit is on.

Should i try an trace the hot water side back to the two value, or would the back feed activate it too.

Thanks
 
Just looked again at your diagram. Seems you have timer in Parallel with Stat.

Generally you'd wire in series. So Timer passes 'on' signal to stat, if water is cool, stat will pass on signal to valve. Valve then opens, activates microswitch, and sends fire signal to boiler.

Not sure if I fully understand the setup though. Got any model numbers and a system schematic?
 
  • Thread Starter Thread Starter
  • #14
Hi There

Thank you for your help.

I have attached the boiler manual and from i read there is no pump overrun or dual inputs for the CF or HW. Just a mains 240v connection. All other switching is controlled externally. If this makes sense.

Apologies the rough sketch i provided is to basic.

On the hot storage CH side i have repol tlr2 controller.

On the hot water clock HW side i have the horstmann xl27 which activates a value system and motor. These are not in the sketch, so apologies, but they are series linked. As if the value is open the pump for the HW kicks in only if the cylinder stats require them. So all is good there.

Just trying to solve the back feed. Cant figure out why i need to do it this way as a dual input on the boiler would have been so much easier.

Is there a external dual input available on the market at all.

Thanks again
 

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