Switch ampacity question

[RatherBeFishin]

Is there anywhere in the code that illicitly says it’s acceptable to use a larger switch than ckt rating on a circuit? Ex. Using 20 amp toggle switches throughout a house on 15 amp lighting ckts

It’s done pretty commonly with disconnect switches being rated for up to 60 amps being used on a 20 amp circuit let’s say

I know to never go the other way of course with let’s say 15 switches than on a 20 amp rated ckt although some argue it’s fine, but does anyone have a reason or code section that says to not use larger switches than circuit rating? As far as I know it’s just like using larger wire than needed on a ckt but could be wrong

 

[James L]

I can't think of anything prohibiting it,
but I can think of a few scenarios where a switch larger than the circuit would be a necessity.

You mentioned a 60 amp disconnect on a 20 amp circuit, But even more common would be a 60 amp disconnect (safety switch) on a 40 amp circuit. You certainly can't put that on the 30 amp disconnect, and have no options in between

 

[winnie]

If you go to _extreme_ aspects of this, you can encounter design problems (not code violations).

For example, if you use an oversized switch (say a 20A light switch) to control logic level signals (milli or micro amps at 5V) then you can have problems with insulating oxide layers forming on the contacts and the signal not being able to punch through them.

-Jon

 

[infinity]

I know to never go the other way of course with let’s say 15 switches than on a 20 amp rated ckt although some argue it’s fine, but does anyone have a reason or code section that says to not use larger switches than circuit rating? As far as I know it’s just like using larger wire than needed on a ckt but could be wrong

A 15 amp snap switch is permitted on a 20 amp circuit as long as the connected load on the switch doesn't exceed its rating. Similar to 600 watt rated dimmers used on 15 and 20 amp circuits.

 

[texie]

If you go to _extreme_ aspects of this, you can encounter design problems (not code violations).

For example, if you use an oversized switch (say a 20A light switch) to control logic level signals (milli or micro amps at 5V) then you can have problems with insulating oxide layers forming on the contacts and the signal not being able to punch through them.

-Jon

Indeed. See this sometimes with switches used on fireplace power pile circuits.

 

[david luchini]

But even more common would be a 60 amp disconnect (safety switch) on a 40 amp circuit. You certainly can't put that on the 30 amp disconnect, and have no options in between

What about a 40A circuit for a 5HP, 208V, 3ph motor? I can't see any reason the motor disconnecting means couldn't be a 30A disconnect.

 

[James L]

What about a 40A circuit for a 5HP, 208V, 3ph motor? I can't see any reason the motor disconnecting means couldn't be a 30A disconnect.

That wouldn't be a 40 amp circuit. That would be a 20 amp circuit.

 

[david luchini]

That wouldn't be a 40 amp circuit. That would be a 20 amp circuit.

How would a circuit with a 40A OCPD be a 20A circuit?

Instead...A 40A branch circuit supplying two 3000W, 240V single phase water heaters. With separate 30A disconnect switches at each water heater.

 

[James L]

How would a circuit with a 40A OCPD be a 20A circuit?

Instead...A 40A branch circuit supplying two 3000W, 240V single phase water heaters. With separate 30A disconnect switches at each water heater.

I think you're straining the question of the OP

 

[ggunn]

I think you're straining the question of the OP

It's what we do, innit?

 

[david luchini]

I think you're straining the question of the OP

I don't know...the OP specifically mentioned NOT putting switches with rating lower than the circuit rating on such circuits, as did you.

The Code doesn't have any such general prohibition.

 

[RatherBeFishin]

A 15 amp snap switch is permitted on a 20 amp circuit as long as the connected load on the switch doesn't exceed its rating. Similar to 600 watt rated dimmers used on 15 and 20 amp circuits.

Right I’ve seen that code. Was more curious about using a 20 amp switch on a 15 amp ckt, logic says go for it because it’s rated for 20 amps so it can handle 15 amps through it. I just like to see it in the code as acceptable but don’t see anything about using larger switches or wire for that matter in the code

 

[infinity]

I just like to see it in the code as acceptable but don’t see anything about using larger switches or wire for that matter in the code

Positive wording as you've suggested is not necessary because these things are written as the minimum standard. Besides electrically what would be the downside of using a 20 amp rated switch on a 15 amp circuit? 20 amps is the maximum rating.

 

[RatherBeFishin]

Positive wording as you've suggested is not necessary because these things are written as the minimum standard. Besides electrically what would be the downside of using a 20 amp rated switch on a 15 amp circuit? 20 amps is the maximum rating.

I don’t suppose any besides a couple of bucks. Just was taught to match ckt size to proper size wire, devices but no harm in my eyes using em if you have them. Larger wire in the middle of a circuit just cause you have it is a bit risky though

 

[RatherBeFishin]

I don’t suppose any besides a couple of bucks. Just was taught to match ckt size to proper size wire, devices but no harm in my eyes using em if you have them. Larger wire in the middle of a circuit just cause you have it is a bit risky though

IMO the wire range on the device tells you 14-10 awg so that tells you what’s acceptable

 

[infinity]

Just was taught to match ckt size to proper size wire

That's not required either. Some think that it's a good practice but in the NEC doesn't care as long as the smallest section of the run has a conductor ampacity that is greater than or equal to the OCPD ahead of the circuit. Where voltage drop compensation has been applied you may see conductors several sizes larger than the minimum required for the circuit and that is perfectly normal. Motor and AC units would be another area where the OCPD is likely to be larger than the ampacity of the conductor.

 

[RatherBeFishin]

Ckt is limited to 15 amps though so 20 amp switch is definitely pointless I suppose lol

 

[RatherBeFishin]

That's not required either. Some think that it's a good practice but in the NEC doesn't care as long as the smallest section of the run has a conductor ampacity that is greater than or equal to the OCPD ahead of the circuit. Where voltage drop compensation has been applied you may see conductors several sizes larger than the minimum required for the circuit and that is perfectly normal. Motor and AC units would be another area where the OCPD is likely to be larger than the ampacity of the conductor.

Agreed!

 

[ggunn]

Larger wire in the middle of a circuit just cause you have it is a bit risky though

Why? We do sort of thing that for voltage drop. As long as all the wire in the circuit has enough ampacity for the OCPD it can be as large as you like.

 

[Jraef]

There is no Code prohibition against using switches rated for MORE amps than necessary. Nor is there a technical reason to worry about it. The only affect it has is on the project cost.

On the side issue regarding disconnect switch sizes, it’s important to note that on motor circuits, the switch must bear a Hp rating equal to or greater than the motor it is feeding. Amp rating is less relevant and in fact is IRRELEVANT if there is a lower HP rating than you think it should be, which happens sometimes.