AC- Live and Neutral Swapping feature - Help needed

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nramesh

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Hi,
I wanted to add one more feature to my present design.But i am not sure whether such feature is feasible ... I need your support in the regarding...

My design application is similar to remote power switch... Load can be any appliance (up to 2-5 A current rating.) I am using SSR relay to switch on/off the load. Prototype works fine without any issues. But there is one practical issue ( here in india ). Sometimes live and neutral gets swapped in wiring...
I have seen many appliances like TV supports such live-neutral swapping.
Is there any circuit/devices present to support such feature?
I would like to address following concerns...
1.There should not be any damage to appliance.
2.There should not be any damage to my internal AC- DC converter section ( which is the power source for micro controller section).
3.Even in worst possible failure case, there should not be any fireworks...
Looking forward to your valuable response...

Regards,
Ramesh
 

Provided that safety is not compromised, it makes little difference which way around the live and neutral are connected. One manufacturer in the UK, where the wiring is very reliable, intentionally puts the SSR in the neutral wire, others put it in the live wire. The equipment doesn't really care as the polarity is reversing anyway but obviously you should ensure that if you isolate the neutral, none of it can be touched as the whole circuit will assume live potential.

Brian.
 

If you are wanting to protect your DC circuitry from this condition you describe, the answer is simple, use a 4 diode bridge. If the polarity is one way, two diodes conduct, if the polarity is the other way the other two diodes conduct. The end result is that with a bridge you can feed DC of either polarity to it and DC of a known polarity will result. Not sure if this will help you in your situation, but it was what came to mind when I read your post.

BTW, new member here, 1st post.

Regards,

Bob
 
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I remember, that old tube radios and tvs with direct mains supply took advantage of live and neutral swapping, particularly when you connected a record player. But do you find them outside a museum?
 

nramesh said:
But there is one practical issue ( here in india ). Sometimes live and neutral gets swapped in wiring...
Click to expand...

It is not a fault of India. It is your fault.
 

FvM said:
I remember, that old tube radios and tvs with direct mains supply took advantage of live and neutral swapping, particularly when you connected a record player. But do you find them outside a museum?
Click to expand...
Not exactly, but there's still a lot of consumer goods and professional equipment with figure-of-eight mains inlets which can be connected either way round. Much of it is found in audio & video equipment where it will be interfaced with other equipment in public places.
But the days of connecting 'the chassis' to either of the mains terminals are long gone (I think and hope!)
 

I'm not quite sure which kind of equipment you're referring to. The question is, if some of these devices have an asymmetrical mains connection, that would e.g. cause considerably different leakage currents at exposed connectors or a metallic surface. Or electrical stray fields affecting the operation. As long as the leakage currents comply with safety standards, it won't be problem, of course. If any of these appliances needs to be plugged in "right" to work correctly (e.g. play music without hum), it's a matter of bad design, I think. So I still doubt the necessity of the questioned swapping device.
 

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