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Curt Welch

(Curt Welch) wrote:

I feel the need to go wire a few 15 amp switches in parallel and see what
type of current balance I actually get.....

Couldn't find any switches digging in the basement but I did a quick test
with a little different format just to see what would happen.

I used 4 wires to connect a standard 20 amp electrical outlet. 2 for the
hot, 2 for the neutral, and then wired those two together to create a
parallel power feed to the outlet. I used standard 12 gauge wire for all
paths. I plugged in a 100 W light to the outlet an measured the current
with a magnetic pick up style AC current meter.

The total current was around .81 amps, and the distribution in the two
parallel paths was around .31 amps and .48 amps or about 40% 60% balance of
current.

I suspect with the contacts of a 15 amp switch, the distribution could
easily be less balanced even with a new switch, and would only get worse
over time as one switch would no doubt wear down faster than the other.
But I don't have one handy to find out if this is true or not.

If you got a 40% 60% split like I did in my quick test, that would be 8.4
amps of your load in one contact and 12.6 amps in the other putting it well
within the 15 amp range of that switch. As long as it stayed that good or
better, it would be fine.

But this just demonstrates how parallel low resistance paths don't tend to
split the current evenly because the resistance is never very close to
equal.

People mentioned the idea of wiring relay contacts in parallel. That's
interesting and makes me wonder why they do it because it would be so hard
to balance the current when the contacts are closed. I wonder if it has
more to do with what happens as the circuit is opened and the contacts arc?
The current through two arcs might be better balanced because of the higher
resistance of the arcs and it might help reduce the spacing required to
break each arc?

Or maybe it's done just to improve relay life by creating redundancy? If
the contacts tend to degrade with age and their resistance increase the
redundant contacts will simply keep the circuit working longer because both
contacts will have to degrade to a high level before the relay will fail to
do its job? I doubt that current load balancing is the main reason for
wiring the contacts in parallel.

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Curt Welch http://CurtWelch.Com/
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