Electric Welder OCPD

[dvcraven0522]

I need some help with OCP for individual welders. I have attached a specification sheet from the manual.

I had design to 90 amp CB. This was a project I did some time ago and now finally under construction. I been asked to review the submittals for the gear.

I have reviewed NEC 630 but still confused if something less than 90 amp breakers would be acceptable. The spec. say maximum effective supply current is 34.1. I am thinking I can use a 35-40amp breaker. It as list minimum conductor size #8awg. But, the maximum Time-delay fuse is 90 so the #8 wire is now not protected.

Thanks.

 

[Dsg319]

Without looking into your picture (will when I get time) electric arc welders can have a certain percentage larger OCPD than the circuit wiring such as motors, transformers and such.

 

[Dsg319]

Can’t see how it could be wrong based off of Manufactures instruction. When sizing circuits to transformer type welders duty cycle is also taken into the calculations which I’m sure they have done. Therefor allowing larger breaker for probably inrush currents while wire is still protected against SC/GF and should be fine as long as the user follows the duty cycle of the welder.

Been a while since I done these calculations. Someone with more knowledge will chime in.

 

[topgone]

Can’t see how it could be wrong based off of Manufactures instruction. When sizing circuits to transformer type welders duty cycle is also taken into the calculations which I’m sure they have done. Therefor allowing larger breaker for probably inrush currents while wire is still protected against SC/GF and should be fine as long as the user follows the duty cycle of the welder.

Been a while since I done these calculations. Someone with more knowledge will chime in.

NEC says (630.12) OCPD should be "no more" than 200% of the rated primary current of the welder unit or I_1max (use the rated primary current is I_1max is not given). AWG #8 is rated 50A so using an 80A OCPD is not beyond 200% of the conductor rated ampacity!

 

[Dsg319]

NEC says (630.12) OCPD should be "no more" than 200% of the rated primary current of the welder unit or I_1max (use the rated primary current is I_1max is not given). AWG #8 is rated 50A so using an 80A OCPD is not beyond 200% of the conductor rated ampacity!

That would be my take on it. Wonder why primary current and duty cycle is not given.

 

[topgone]

That would be my take on it. Wonder why primary current and duty cycle is not given.

As mentioned, if I_1eff is not given, we can use the rated primary current of the welder unit in sizing the OCPD. If we wanted to know the effective current of the welder at a certain duty cycle, the formula is given as:
I_eff = square root [(I².X +Io².(1-X)],

where; I = welder amps and Io = no-load amps of welder unit.​

But that is not be needed when designing the feeder for welder/s.
Unless the welder unit is automatic and has its own sequence of operation, one cannot be sure of the duty cycle as techs don't the same ways of doing welding.

 

[Dsg319]

As mentioned, if I_1eff is not given, we can use the rated primary current of the welder unit in sizing the OCPD. If we wanted to know the effective current of the welder at a certain duty cycle, the formula is given as:
I_eff = square root [(I².X +Io².(1-X)],

where; I = welder amps and Io = no-load amps of welder unit.​

But that is not be needed when designing the feeder for welder/s.
Unless the welder unit is automatic and has its own sequence of operation, one cannot be sure of the duty cycle as techs don't the same ways of doing welding.

I’m not 100% sure what your saying about duty cycle. But duty cycle is not how much the person chooses to use it, but rather a percentage they can use it in a allotted amount of time. And is usually listed on the welder itself.

 

[Dsg319]

630.12 over current protection for welders

630.12 over current protection- Overcurrent protection for arc welders shall be as provided in 630.12(A) and (B). Where the values as determined by this section do not correspond to the standard ampere ratings provided in 240.6 or where the rating or setting specified results in unnecessary...

forums.mikeholt.com

 

[Hv&Lv]

If I’m reading the op correctly, he has all the provisions there for a 90 amp breaker, but wants to install a smaller breaker?
Does the NEC say you shall protect at the max?

If I install #12 to all my outlets, use 20 amp outlets, yet want to protect it at 15 amps, thats acceptacle.

 

[Fred B]

I need some help with OCP for individual welders. I have attached a specification sheet from the manual.

I had desigen to 90 amp CB. This was a project I did some time ago and now finally under construction. I been asked to review the submittals for the gear.

I have reviewed NEC 630 but still confused if something less than 90 amp breakers would be acceptable. The spec. say maximum effective supply current is 34.1. I am thinking I can use a 35-40amp breaker. It as list minimum conductor size #8awg. But, the maximum Time-delay fuse is 90 so the #8 wire is now not protected.

Thanks.

To start with what supply voltage you dealing with? Makes a difference. If highlights are your's will assume 3phase.
Spec sheet indicates:
Max overcurrent 90A if time delay 100A standard breaker or fuse. So simply can't use a breaker any larger than, likely welder is not listed to handle more.
Minimum effective supply of 34.1A basically indicates nothing less than will work as equipment may not perform as needed. Can be installed up to the maximum breaker size listed of 90A if time delayed or 100A standard non delay breaker.
Minimum conductor size is just that, minimum. Size of the conductors, or the reverse, the size of breaker must be sized to each other in compliance to code. If you are opting for the 90A breaker wire must be sized to it; if sizing to minimum breaker, size wire to it.
See final note #4 of listing you attached for further conductor size guidance here it points you to Articles 310 and 400 depending on you wiring methods.
Personally I would not go to the minimum size as that would be asking for nuisance tripping.
Other consideration that is not found within spec sheet is related to what is existing sevice capacity?

 

[dvcraven0522]

Thanks for all of the responses. I am going to leave the 90 CB with #8.

 

[hillbilly1]

Tend not to download files from unknown source, so I haven’t seen the type of welder in question. If it is a spot welder, it usually will have a higher ocp setting due to higher inrush currents for short periods of time than a standard welder.

 

[topgone]

Tend not to download files from unknown source, so I haven’t seen the type of welder in question. If it is a spot welder, it usually will have a higher ocp setting due to higher inrush currents for short periods of time than a standard welder.

As mentioned, 200% of the primary current of the welder is the limit in sizing OCPD for the welder unit or 200% of the conductor ampacity. Methinks the engineers before us have studied these and has proven this rule as safe and practical.

 

[ActionDave]

.....Minimum conductor size is just that, minimum. Size of the conductors, or the reverse, the size of breaker must be sized to each other in compliance to code. If you are opting for the 90A breaker wire must be sized to it; if sizing to minimum breaker, size wire to it.

Conductors for welders are not subject to the same rules as other circuit conductors. You could legally and safely put 8 AWG conductors on a 90 amp breaker.

 

[hillbilly1]

As mentioned, 200% of the primary current of the welder is the limit in sizing OCPD for the welder unit or 200% of the conductor ampacity. Methinks the engineers before us have studied these and has proven this rule as safe and practical.

The reason for the high spot welder ocp is because the current is much higher than a standard welder, but it is only for a very short period of time. The first one I had hooked up called for a 200 amp ocp, with only #2 feeding it. The engineer explained how it works. I had ran 2” pvc (engineer said not to use emt because of the high current, that metallic conduit would choke the current, and the welder would not work well) The one problem I found, was I should have ran the smallest conduit conduit allowed for the #2’s. Every time it did a weld, the wires would slap pretty hard in the conduit.