One light from two power sources

[Marnhullman]

I have electrically operated doors on my double garage which is at the far end of a workshop that is accessed from the house. When either garage door is operated a courtesy light is illuminated on the appropriate unit but the light only covers a small area not including the walkway through the workshop.

I have in mind to take a power supply from each door light and connect them to a slave light further up the workshop. However, I can't figure out how to wire the slave unit so that only it and the active door light are lit i.e. if both door units are wired to a single slave then the non-active door light will illuminate as well because the wires will be joined at the slave light. Hope this makes sense?

Is there a junction box or switch available that can help me achieve what I want? If it were a 12v system then I could use a brake/tail ight with dual filaments and wire each door light separately...

Thanks for any advice.

 

[bernardgreen]

You can use a pair of relays.

Connect the coil of a relay to each courtesy lamp so the relay operates when the lamp is lit.

Connect a pair of normally open contacts on one relay in parallel with a pair of normally open contacts on the other relay.

Use these as the switch for the slave lamp.

 

[Marnhullman]

Thanks to bernardgreen

Just started looking for relays - there seems to be an awful lot available and all with multipins. Can you give some specific advice re. description of type I should look for? Also normally open contacts?

Can you point me to suitable components available in the UK on the web?

Thanks

 

[bernardgreen]

As soon as I get a free minute ( probably tommorrow ) I'll dig out the information for you

 

[ban-all-sheds]

if both door units are wired to a single slave then the non-active door light will illuminate as well because the wires will be joined at the slave light.

Why is that such a problem that you want to go to the trouble and expense of putting in relays?

 

[westie101]

I would have thought it easier, less complicated and possibly cheaper to just put 2 new identical light fittings side by side

 

[bernardgreen]

Westie's idea is a good one. There may be fittings that have two separate lamp holders in them.

If want to use just one lamp then there are two suggestions.

If both Live and Neutrals for the existing lights both come from the same circuit ( both connected to the same MCB in the consumer unit ) then the one relay solution is OK

If the two existing lights are supplied by different MCBs then the two relay solution is better. The one relay solution will also work but has the risk of tripping one or both RCDs as the relay changes state. ( the lamp may be transiently connected to a live from one supply and to the neutral of the other supply )

Relays are octal based 230 volt AC coil, 2 pole changeover (DPCO)

RS components 348-762 and the base 403-213
( other supplies are available )

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• bernardgreen
• 28 Apr 2011
• 1

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• bernardgreen
• 28 Apr 2011
• 1

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• bernardgreen
• 28 Apr 2011
• 1

I have just spotted my deliberate error

In the single relay solution La and Lb are the switched lives from the existing lamps. That is correct,

In the two relay solution La and Lb to the relay coils are the switched lives from the existing lamps. The live feed to the contacts feeding the lamp is the PERMANENT live from either of the existing lamp controllers, the neutral for the lamp must come from the same circuit as the permanent live.

 

[Marnhullman]

Thanks to all.

Thought about Westie's idea but hoped there was an easy (and cheap!) method of just having one lamp. The relays etc. seem overly complicated so will either just have one lamp from the most used door closer or double up and put in two lamps.

Again, all contributions much appreciated.

 

[holmslaw]

..

 

[ban-all-sheds]

It isn't two sources - it's a single source with 2 switches in parallel operating the lights.

 

[holmslaw]

..

 

[ban-all-sheds]

You are really desperate to show your stupidity, read the latest proposal.

This is the latest one:

The relays etc. seem overly complicated so will either just have one lamp from the most used door closer or double up and put in two lamps.

To the op you need a label to advise the presence of two supply sources.

Which are the two supply sources?

 

[bernardgreen]

The there is a supply from each of the two existing courtesy lights. They may not be from the same MCB and may be from different consumer units.

 

[ban-all-sheds]

That's quite true - there could be 2 circuits, and they could be from 2 different CUs.

They could also be on 2 different phases, which would be spectacular if connected together in the way the OP envisages.

All unlikely, but all possible.

So are we to take it that holmslaw has been on site, and carried out an inspection, and knows that they are on different sources but the same phase?

After all - he is adamant that this is the case.

The two supply sources create a potentially dangerous situation.

You should fit a permanent sign stating that the two lamps are fed from different sources.

To the op you need a label to advise the presence of two supply sources.

 

[securespark]

Are you two brothers with unresolved familial issues?