6-20R breaker size

[Leespark57]

Hello all,

A 3hp 230 volt dust collector came equipped with a 6-20P cord cap from the factory. Table 430-248 has the FLC at 17 amps, creating a red flag for me. However when the unit is plugged into a 6-20R receptacle on a 2 pole 20 it trips within 10 seconds from the inrush current (approx 55 amps on the meter). When diagnosing the problem a 30 amp breaker was installed to check the current. The 30 amp breaker held during inrush and leveled off at 14-15 amps. Is it permissible to install a larger size breaker per Table 430.52 (up to 250%) on an individual branch circuit feeding a single 6-20 receptacle? I would rather not cut the cord and hardwire potentially voiding the listing of the equipment.

Thanks

 

[infinity]

You cannot use a 30 amp OCPD with a 20 amp receptacle. The unit should run based on a circuit that is the same as the cord cap.

 

[hillbilly1]

If it is a Square D QO breaker, you will need to change it to a QOHM (high magnetic). QO’s 20 amp and under do not like motor loads that are sized close.

 

[Leespark57]

Would a standard plug in breaker, Siemens in this case, be expected to withstand that type of inrush current? I'm assuming these are considered inverse time circuit breakers??

 

[winnie]

I see references to Siemens Q220HM breakers, but can't find any specific info in a siemens product catalog.

-Jon

 

[infinity]

I had a new compressor (15 amp plug) in my old garage that ran for a few years on a 20 amp individual branch circuit. Then it started to trip the 20 so I just installed a 30. Never tripped again. When I moved I put the 20 back in and then I put the compressor in my new garage. Now it will trip the CB about 1 in 10 times on start up and the circuit is only 15 amps. The old garage had QO breakers, the new garage Siemens. Go figure.

 

[zbang]

I'd be calling the manufacturer, if nothing else for giggles, to ask how they think it should be installed & protected.

 

[kwired]

If it is a Square D QO breaker, you will need to change it to a QOHM (high magnetic). QO’s 20 amp and under do not like motor loads that are sized close.

That only applies to the single pole 15 and 20 amp breakers. Those have lower magnetic trip setting than same thing in 2 and 3 pole units.

There is no "HM" breaker in any other QO size/number of poles units.

 

[kwired]

That only applies to the single pole 15 and 20 amp breakers. Those have lower magnetic trip setting than same thing in 2 and 3 pole units.

There is no "HM" breaker in any other QO size/number of poles units.

And quite frankly they should have just made everyone else make similar magnetic trip on theirs instead of making us use AFCI's.

 

[Tulsa Electrician]

System voltage?
Just curious

 

[kwired]

System voltage?
Just curious

After OP greeting, third word in his post.

OK that is equipment voltage, but one must sort of assume it is on a 208 or 240 volt system.

 

[augie47]

That only applies to the single pole 15 and 20 amp breakers. Those have lower magnetic trip setting than same thing in 2 and 3 pole units.

There is no "HM" breaker in any other QO size/number of poles units.

(2) SP HM20s with a handle tie

 

[kwired]

(2) SP HM20s with a handle tie

I guess, AFAIK you have same magnetic trip setting as you do with a regular 2 pole 20 amp breaker though.

 

[petersonra]

(2) SP HM20s with a handle tie

A handle tie does not make them common trip though and that would be a requirement I think for a 2 pole circuit.

 

[kwired]

A handle tie does not make them common trip though and that would be a requirement I think for a 2 pole circuit.

IIRC, there is less limitation than many think on this.

compare to a two pole fused switch, you can blow one fuse but not the other, yet the switch (handle tie with the breaker) still makes it simultaneous disconnection of both poles and is still suitable for a disconnecting means.

 

[augie47]

A handle tie does not make them common trip though and that would be a requirement I think for a 2 pole circuit.

240.15(B)(2)

 

[david luchini]

A handle tie does not make them common trip though and that would be a requirement I think for a 2 pole circuit.

I think 240.15(B)(2) would permit the handle tie.

Edit: Gus is too fast.

 

[petersonra]

I think 240.15(B)(2) would permit the handle tie.

Edit: Gus is too fast.

I think he is right.

 

[kwired]

IIRC, there is less limitation than many think on this.

compare to a two pole fused switch, you can blow one fuse but not the other, yet the switch (handle tie with the breaker) still makes it simultaneous disconnection of both poles and is still suitable for a disconnecting means.

240.15(B) (2) and (3)

Note that 240.15 does have informational note to see parts of art 430. Only thing I found there would be maybe if you are providing motor overload protection with the breaker (not real common situation) that you might need common trip on a three pole breaker, otherwise two pole line to line volt motor would still interrupt motor current if only one pole trips.

Once you get over 30 amps availability of single pole breakers is maybe more of a factor in selecting two or three pole common trip units over multiple single pole breakers and handle ties.

Gus beat me to providing a code section, though I think I got sidetracked a little an never noticed his response.

 

[Tulsa Electrician]

The reason I ask was he used the table. If from a 208 system it would be higher.
Then my next question would be name plate of motor.
Then next question would the allowable ampacity on the 20 amp single receptacle.
If was a house I would have assumed 240
Thanks for your reply.