Relay Wiring

[Phillay]

Hi guys, need some advice.

Have a condensate pump to wire up. The pump has a safety switch cable (1 blue, 1 brown wire) that is to be wired into the 'permanent live' to a combi boiler. Therefore, if pump failure occurs, the combi will be shut down (as it condenses in both H and DHW).

The cable size of the safety switch is 0.5mm... but the boiler manufacturers have specifically stated the power to the boiler must by wired from the 3 amp fuse in 0.75mm and it's not acceptable to drop to 0.5mm to incorporate the switch.

Can't upgrade the safety switch cable and so the boiler manufactures have suggested I could use a relay to supply the boiler and the condense safety switch cuts the relay if pump failure occurs (this will mean the boiler is still continuously fed by 0.75mm).

Been putting this off for a while as I haven't got a clue as to what type of relay to use and how this would be wired up.

Cheers.

 

[Leesparkykent]

What make is the condensate pump?

 

[Phillay]

Grundfos... it's a conlift 1

 

[snowhead]

What Boiler is it?

I can't see the condensate switch being used to isolate the power to the boiler as that would prevent pump over-run to cool the heat exchanger down.

I would have thought it would just have safety circuit connection to inhibit the burner.

 

[Phillay]

Boiler is Worcester Bosch Greenstar Compact. Worcester themselves advised:

"[FONT=&quot]You would need to have the pump wired into permanent supply to the boiler so if there was a failure the boiler would be isolated completely making it impossible to produce any more condense. Having it wired across the LS & LR connections would mean that the boiler would not fire for heating but it would for hot water, so the boiler would still be producing condense which could back up to the boiler and given enough time cause damage to the boiler."[/FONT]

 

[davesparks]

What Boiler is it?

I can't see the condensate switch being used to isolate the power to the boiler as that would prevent pump over-run to cool the heat exchanger down.

I would have thought it would just have safety circuit connection to inhibit the burner.

It's a combi boiler, there's no way to inhibit the burner without altering the internal wiring of the boiler.

 

[Phillay]

Just to clarify (incase I haven't!), the safety switch on the condense pump will only operate (break the circuit) in the event of a the pump water level getting too high.

 

[snowhead]

It's a combi boiler, there's no way to inhibit the burner without altering the internal wiring of the boiler.

I was suggesting the manufacturer would already have the option of a safety circuit connection but judging by their statement they haven't.

 

[davesparks]

I was suggesting the manufacturer would already have the option of a safety circuit connection but judging by their statement they haven't.

Does any domestic boiler have such a connection? I can't say I've ever come across one yet.

 

[Phillay]

Doesn't appear they do... it's pretty frustrating really.

Worcester state the cable from spur to boiler must be a continuous size of 0.75mm, yet it's only on a 3 amp load.

The safety switch cable may only be 0.5mm, but Grundfos install instructions state the safety switch can handle a max of 5 amps.

All in the all, I would expect the 3 amp fuse to blow way before the 0.5mm cable would melt... but Worcester are basically telling me any drop in the cable size is unacceptable and would cause warranty issues.

Nice of them to offer up the idea of a relay, but I'm in the dark on that one.