How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Michael Your Own Question
Michael, Home Appliance Technician
Category: Home Improvement
Satisfied Customers: 9568
Experience:  Home Appliance Technician
Type Your Home Improvement Question Here...
Michael is online now

I have a Round-base 10A Relay 12V DC 3PDT and a Round-base

This answer was rated:

I have a Round-base 10A Relay 12V DC 3PDT and a Round-base 10A Relay Socket 11-Pin, I wish to use them to simply switch on a 240v extractor fan from a 12v Dc lighting circuit. I am however baffled as to where the connections 'go'.
The supplies are:
a switched 12v DC +ve and -ve circuit from a 12 LED lighting ciruit
a 240v supply from a household lighting circuit.
Hi and thank you for choosing Just Answer.
I am Tech Michael and I will be assisting you today.
Please be patient as these are technical questions that may require a bit of conversation to solve. Also remember to be detailed in your description of the problem. That will help me make a diagnosis quickly for you.
You will need a mutimeter to do some testing on this relay, do you have one?
Thank you
Tech Michael
Customer: replied 2 years ago.

Yes I have simple one but with all the usual funtions.

Hi Peter,
the first thing you need to do is figure out which two pins are the coil that activate the relay these will be non polarity sensitive in most case. Let me know when you have that part figured out.
Customer: replied 2 years ago.

Sorry for the delays, but I'm in the middle of fitting out a kitchen!

I've sussed out the coil circuit which it states is 12v on the relay case, so as long as the relay is activated (it won't matter which is + or - (as I remember from my physics). The other nine pins are activated in batches of 3 for each of the three switches in the following sequence live,common and switched. These are shown on the semi-transparent case as being 240v, so I presume as I only want one relay to activate I can use any one of the three with a live in and live switched out.

Of choice I can use one side of the socket for 12v and the other 240v keeping them well apart. I'll then house the unit in an insulated 'box' for safety reasons.

Does this sound sensible? Sorry for the non technical lingo, I was a chartered civil engineer not electrical as I'm sure you can tell.



Hi Peter,yes you are doing things well so far;-)
Next let me know if you need the contacts to be open or closed when the relay is at rest or active? Let me know. Baiscally you just can check with your meter to see which ones open and close as you apply power to the relay and there you ahev it. Usually the opposite contacts will be normally closed (at rest) no power to the coil.
And that should do do it.
I will stick with you until your understanding of the relay contact is what you need to know;-) and is working correctly,and it won't cost you anything additional to rate my service. You can always get in touch with me if you need further assistance after rating;-)
Thank you and have a nice weekend;-)
Michael and other Home Improvement Specialists are ready to help you
Customer: replied 2 years ago.

Hi Michael,

I've sussed out which set of 3 contacts I am going to use to enable me to keep the 12v system well away from the 240v.

I'll attach the Live 240v cable to the common terminal of the set and the N to the at rest contacts. Thus when the 12v is applied the coil will make the contact active and hence switch on the 240v supply.

I'll keep you posted as I hope to do the installation tomorrow.



Customer: replied 2 years ago.

It's done and working!

Ta for the pointers.


Awessome Peter!