Can you change the wire gauge if relay used?

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  #1  
Old 09-17-14, 12:53 PM
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Can you change the wire gauge if relay used?

Just inspecting the breaker panel, I've seen a 30A breaker connected to a relay, which states 220-240V 22.5 ANI (i assume that's 22.5A)?
Out of that relay then comes AWG 12 guage wire instead of 10/2 that should be on a 30A breaker.
Is that acceptable or should the electrician have put in 10 guage?
 
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Old 09-17-14, 02:39 PM
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Yes it should be #10 or the breaker size reduced in most cases but there are exceptions such as A/C compressors.
 
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Old 09-17-14, 03:31 PM
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The #12 might be the control circuit for the relay and on a different circuit. The relay might be switching the 30 amp circuit. Turn off the 30 amp breaker and see if the relay can still be activated.
 
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Old 09-17-14, 03:51 PM
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The wire from the panel goes straight into the bottom of relay and then 2 x #12 out the top of it.
When I turn the breaker off, and turn t-stat up, the relay does not click.
 
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Old 09-17-14, 03:55 PM
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Ah, it sounds like a relay with a 24 volt coil. In that case, the wire should be #10, or the breaker should be 20 amp or less.
 
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Old 09-17-14, 04:01 PM
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Strange. I'm trying to figure out why an electrician would have used #12 then.
The circuit is 4500W so realistically it's never going over 18A or so but still.
 
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Old 09-17-14, 05:23 PM
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4500w at 240vac = 18.75A
There should only be a continuous load of 16A maximum on a 20A breaker.
The 20A breaker was probably tripping after the heaters were on for a while.
 
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Old 09-18-14, 01:44 PM
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Doesn't the code require 10AWG for a 30A breaker though or is it acceptable to upgrade a breaker from 20 to 30 and use existing wiring if the load on the circuit is not expected to be above 20A?
 
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Old 09-18-14, 04:10 PM
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It is not acceptable to use a breaker of more than 20 amps on a circuit with 12 or smaller gauge wire.

If the load is not expected to be above 20 amps then the 20 amp breaker will pose no problem.

You may not hard-wire continuous duty classified equipment such as heaters or air conditioners with total load more than 80% of the circuit amperes wise. For example a maximum of 16 amps (either 120 volt or 240 volt) worth of built in heaters may be wired to the 12 gauge (max. 20 amp) circuit.
 
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Old 09-18-14, 04:21 PM
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Is it possible that with a relay in the middle limiting to 22.5 amps this might be allowed somehow?
I assume the relay doesn't have an internal breaker/fuse.
 
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Old 09-18-14, 04:34 PM
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With the relay's controlled circuit (connected to the relay contacts) limited to 22.5 amps you may have a maximum of a 22.5 amp breaker (round down to standard size 20 amp breaker) in the panel for the branch circuit feeding the loads controlled by the relay. So the subject of 10 gauge wire does not come up except when dealing with voltage drop in long runs. A relay does not limit the current in its controlled circut but rather an appropriate breaker (such as in the panel) is needed to prevent loads from drawing too much current through the relay contacts and burning out the relay.

The relay's controlling circuit (feeds the relay coil) may or may not require a different voltage and typically needs to supply just a fraction of an ampere. If 120 or 240 volts, the feed may be a subcircuit coming off of a branch circuit up to 20 amps unless otherwise stated in the relay instructions. The coil draws the same tiny current (or nothing with the switch or thermostat in one position) from the controlling circuit regardless of the load in the controlled circuit and regardless of the breaker rating of the branch circuit used to supply the controlling (sub)circuit.
 

Last edited by AllanJ; 09-18-14 at 05:17 PM.
  #12  
Old 09-18-14, 05:11 PM
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Can't because it's 4500W of heaters or 18.75A, which is over the 80% allowance of a 20A breaker.
 
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Old 09-18-14, 05:17 PM
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Are you asking a question or just restating a previous post ?
 
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Old 09-18-14, 05:47 PM
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2. Because it is 18.75 amps withich is over the 80% allowance of the 20 amps rating of the 12 gauge wires wires.

The 80% allowance or 16 amps for 12 gauge wires will be reached at 3840 watts for 240 volt equipment or at 1920 watts for 120 volt equipment.
 
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