Welder spec. requires 50A outlet, 208/3 for connection, but 100A/3P, 208/3 breaker in panel dues to inrush. Welder's full load amp. is around 38A, the inrush current is 78A. However, 100A wires is too large to terminated at 50A outlet, EC suggests to install a disconnect before the outlet to reduce wire size and be able to connect to the 50A outlet. Should the disconnect be fused as fault current at the outlet is more than 10KA? If so, should fuse size match breaker size, i.e. 100A or can be smaller, or = 38A x 1.75 = 66.5A, next standard fuse size is 70A per NEC 430.52?
Welder circuit
- Thread starter anbm
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Do you have a link to this specification? Why would you need a 100 amp conductor on a 50 amp receptacle?
630.12(B) is your financially generous friend.
Hard to understand that 630.12(B) section.
Of course, it's in the NEC
Bottom line is the conductors are usually rated well below the overcuirrent device rating.
If you can provide the particulars for the welder in question I'm sure someone on the Forum can help you size the conductor.
(If it has factory cord and plug rated 50 amp that's likely the key to the allowable conductor size)
Last edited:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You can use an OCPD up to 200% of the circuit conductor size. Since you're using a 50 amp device with a 100 amp OCPD you may only need 50 amp conductors.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
It’s probably a spot welder, those draw high current for a short period of time, that’s why the ocp is high compared to the circuit. Because of its short duration, overheating of the smaller wire is generally not a problem. Most manufacturers call for pvc conduit instead of metal due to the high magnetic field. Also, do not oversize the conduit because the wires will slap because of the magnetic field.
First welder: SRH-444 (outlet at job site: NEMA 14-50R, this is single phase 50A outlet) but data sheet below has 3-phase circuit and 125A fuse required. What is wire size need to be?
Link: https://www.millerwelds.com/files/owners-manuals/o2230h_mil.pdf
Second Welder: Millermatic 255 (outlet at job site: NEMA 6-50R, this is 50A outlet), cutsheet shows 100A fuse required. What is wire size need to be?
Link: https://www.millerwelds.com/files/owners-manuals/O279299C_MIL.pdf
Link: https://www.millerwelds.com/files/owners-manuals/o2230h_mil.pdf
Second Welder: Millermatic 255 (outlet at job site: NEMA 6-50R, this is 50A outlet), cutsheet shows 100A fuse required. What is wire size need to be?
Link: https://www.millerwelds.com/files/owners-manuals/O279299C_MIL.pdf
See below, I just posted.
hmmm, the client sent a picture of NEMA 14-50R outlet was installed, probably wrong manual then...
both welders run at same time, each plugs into its own outlet/circuit.