Current detection on a NEMA 1030 and 1430 circuit using Neutral?

[avid_leaner88]

Hi folk, I am new and hope this is an appropriate question here.

I am designing a contraption that can detect current through a nema 1030 or nema 1430 receptacle.
The appliance plugged into these receptacles typically is a dryer, but I hope principle applies to any appliance.

I have noticed that some newer dryers, when running in power saving/cooling phase, would put load on only 1 of the hots. E.g. 9 amps on one hot, 0 amps on the other.
It becomes a crab shoot if I want to detect current using a hot wire, cause the dryer maybe putting load on the other hot that I am not measuring. Or I would need to measure current on both hots which adds to complexity.

However is it possible to detect the current on the neutral wire? In theory, current should be going through the same(shared) neutral wire no matter which hot has a load on it. I put that to the test, and saw that indeed there is current on the neutral wire when either hots has a load AND when both hots have loads, but it is only 5 amps (via a clamp meter), when I know the load on the hot wires are between 9 to 22 amps.

So my questions are
1. How come only 5 amps is measured when I think there should be more current running through the neutral?
2. Is it reliable to use Neutral as a method for current detection in a 240v circuit?

Thanks!

 

[ptonsparky]

1. The heater is operating at 120v instead of a normal 240v. Less volts equals less amps in a resistive circuit.

2. You have discovered why already. It, the neutral, is not used in a 240v circuit.

 

[winnie]

1 Current must flow in a closed loop from source, through the load and back to the source. At a minimum only 2 terminals are required to do this. Current could flow from either hot to neutral, or from hot to hot completely bypassing the neutral.

2 nope. At a minimum you need to sense at least 2 of the 3 conductors

3 this forum does not permit diy questions, but generally does permit job related questions from non electricians. Since you clearly don't know electrical theory I suggest you partner with someone who does, and focus on the product design aspect of 'what the thing should do'

-Jon

 

[avid_leaner88]

Guys, appreciate the pointers.

 

[avid_leaner88]

An add-on question, since I only want to detect if there is current running through either one of the live conductors and not the accuracy of the current reading.

It is a good idea to make a loop with one of the hot wire, and then read both hot wires at the same time? It should total the current from both wires, thus allow me to detect current with one meter.

Thanks!


suggested in https://www.contractortalk.com/f5/measuring-240v-current-clamp-meter-132088/

 

[synchro]

An add-on question, since I only want to detect if there is current running through either one of the live conductors and not the accuracy of the current reading.

It is a good idea to make a loop with one of the hot wire, and then read both hot wires at the same time? It should total the current from both wires, thus allow me to detect current with one meter.

Thanks!

View attachment 2552789
suggested in https://www.contractortalk.com/f5/measuring-240v-current-clamp-meter-132088/

Yes, by reversing the direction of one of hot wires through the current transformer the magnetic fields of both hot wires will reinforce each other instead of cancelling. And so it will effectively add the currents as you are intending it to do.