Welder Nameplate - Follow or Lead design

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
Just curious if I read this nameplate correctly.
and would you do what is technically correct or what is realistically fine.

I was going to provide some #6 for this 240v 1 ph welder which is about 30 ft from the panel source and
they like to use 100' cords to make their welders more portable.

I figured ( A ) is intermittent ( 60 % ) and steady ( 100% )
( B ) being the amperage of 51A , 60% / 36A, 100%

They have several welders already, I'm providing 3 more welder receptacles (each independent 240 1 phase circuits )
The existing welders all use 50 A Receptacles throughout the shop.

I was just contemplating, do I go with matching their original design based on this existing equipment
or do I get all technical based on the nameplate and have 1 receptacle 60 A rated, therefor no other welders
can use the new receptacles I install, based on the existing cord end configuration.

My questions to you guys is .. would you match the existing design knowing that they are slightly under the welder capability
or do you do what I'd rather do and rate the new receptacles to accommodate the 50 + amp ability.

I'm probably going to just keep the new receptacles at the 50 A rating and hope the additional 1-3 amps wont do much overheating at the plug

welder lable.jpg
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
The IP23 is an "ingress protection" rating where:
the first digit "2" means protected from touch by hands greater than 12 millimeters
the second digit "3" means protected from water spray less than 60 degrees from vertical

I suspect (but don't know for sure) that the I1eff max of 53.5A / 31.6A means that it maintains more than a certain level of efficiency over that range of AC input currents. I don't think it has anything to do with the duty cycles of 60% or 100% because that entry in the table is not partitioned into two parts like it is on the lines above it.

Because the welder regulates its output current, you can see that for a weld current setting of 250A it draws essentially the same input kVA at 208V or 230V:
208V x 57A = 11.8 kVA
230V x 51A = 11.7 kVA

So any additional voltage drop from cords will increase the AC input current for a given welder current setting.
But this should be a relatively small increase in your case:
For example, a 100 ft #6 cord will have 0.08Ω total resistance so that would be a 4.08V drop at 51A or 1.8% of 230V. So the AC current draw will increase proportionally to about 52A because (230V - 4.08V) x 52A = 11.7 kVA.

The welder sticker does not specify, but I would fully expect that if you provide 240V instead of the 230V "utilization" voltage then the input current would go down from 51A to (230/240) x 51A = 48.9A at the 250A weld current setting. Then if you add approximately 1A as above due to the 100 ft cord voltage drop, you are essentially right at a 50A draw.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Te 60% and 100% values are the "Duty Cycle" of the welder. In welders, the duty cycle is always based on a 10 minute use period, meaning that at a 60% duty cycle, the welder will be OFF for 40% of the cycle, i.e. ON for 6 minutes, OFF for 4 minutes. So in this case if they are using it at the 60% duty cycle, it can put out 250A at 60VDC max for 6 minutes before it will shut itself down, and must rest for at least 4 minutes after than. When putting out 250A, it will draw 51A at 230V C input. The 100% duty cycle, meaning continuous welding, is less welding current, so less input current., in this case 36A @ 230VAC. That would be the "continuous" circuit sizing you would use for your receptacles.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
On trip curves of typical QO breakers it takes about 65 seconds to trip at 1.414 times the long term current value at the upper left border of the trip region (this is an increase of 2x in power for I²R heating) . And it takes about 100 seconds to trip at 1.414 times the long term current value at the upper right border of the trip region.
This indicates a thermal time constant of about 1.6 to 2.4 minutes using a simple exponential model.

I assume that these time constants of breakers correspond to what's appropriate for protecting wiring and devices including receptacles. So I think the 10 minute period specified for the duty cycle to protect a welder might not be appropriate for sizing wiring and devices, because the relatively long thermal time constants associated with transformers or inverter heat sinks of a welder allow it to operate at increased current levels over a longer duration before reaching a temperature limit.

For example, the specified 51A current draw at a 60% duty cycle is 1.42 times the 36A at a 100% duty cycle. This produces 2.0 x times the I²R heating power. But if a QO breaker draws more than about 1.15 times its long term trip current value for 6 minutes (60% of a 10 minute period) it will trip. So unless breakers are excessively conservative by having shorter thermal time constants than what's really necessary, I would size things above the current level spec'd at a 100% duty cycle. That's just my judgement based on what I see.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
NEC 630.11(A). Individual Welders. The ampacity of the supply conductors shall be not less than the I1eff value on the rating plate. Alternatively, if the I1eff is not given, the ampacity of the supply conductors shall not be less than the current value determined by multiplying the rated primary current in amperes given on the welder rating plate by the factor shown in Table 630.11(A) based on the duty cycle of the welder.

What confuses me is that there are 2 different values for I1eff. I would think you need to use the higher one since you can't guarantee what duty cycle they will be using. Technically, this forces you to a 60A receptacle and #6 cu wire. You are also allowed to install a breaker much larger than 60A if needed (see 630.12).

Alternatively, you could argue that you're installing various 5-50 receptacles for general use. Put a 50A breaker on them and let that protect the receptacle and wires from overload if they run the welder too hard. The only remaining question to me is whether a 5-50 plug is permitted to be installed on that welder.
 

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
the I1eff
What is this value based on .. and what does eff stand for .. efficiency ?

sorry I missed this from post #3
The IP23 is an "ingress protection" rating where:
the first digit "2" means protected from touch by hands greater than 12 millimeters
the second digit "3" means protected from water spray less than 60 degrees from vertical


Thank you.
 
Last edited:
Top