Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 630, Electric Welders

An electrical engineer designing the load side power distribution for an industrial facility is probably going to include at least a few welding receptacles. It would be a bad idea not to. An electrician may be called upon to replace, upgrade, or add receptacles for electric welders.

When we think of welders, we think of equipment used to join two pieces of metal. And that's typically for repair work. Additionally, a facility may contain process equipment that makes electric welds or that does plasma cutting. The electrical engineer designing the power distribution will have to properly supply this equipment. An electrician may be called upon to replace, upgrade, or add such equipment (with or without engineering supervision).

The code requirements for this work are in Article 630.

  1. Size electric welders supply conductors for an ampacity at least as much as the I(sub)1eff value on the rating plate [630.11]. If this number isn't there, visit the manufacturer's Website to find it. If that doesn't pan out, then you'll have to multiply the primary current shown on the nameplate by the relevant factor shown in Table 630.11(A).
     
  2. What if you have a welding receptacle at every fourth column along the perimeter walls? That ends up being quite a few welders, if you are indeed using all those receptacles. You can apply standard diversity factors; you know, for example, the tenant is never going to have more than 3 welders on the premises so you can base your calculations on intended use and intended duty cycles and get the AHJ to sign off on it.

    But it's unlikely you'll have that exact scenario. More typically, you will have to use the "group of welders" calculation specified in 630.11(B). That means you add together the amperage of the two largest welders, 85% of the third largest, 70% of the fourth largest, and 60% of the remaining welders.

    Just make sure you have enough ampacity for actual use.
     
  3. When you calculate your overcurrent protection, the values might not correspond to the standard ratings in 240.6. In such a case, you can use the next higher standard rating [630.12].
     
  4. The overcurrent rating for each welder cannot exceed 200% of the I(sub)1max [630.12(A)].
     
  5. Conductors supplying more than one welder must be protected by an overcurrent protection device (OCPD) rated (or set) at not more than 200% of the conductor ampacity [630.12(B)].
     
  6. For each welder that doesn't have an integral disconnect, you must install a disconnect for it. And you must identify it as such. The disconnect must be a switch or circuit breaker [630.13].
     
  7. The rating plate must have the eight types of information identified by 630.14. If it doesn't, contact the manufacturer for a replacement plate that does.
     
  8. The electrode and work conductor of an arc welder constitute the secondary circuit of the welder. Don't treat this as premises wiring for purposes of applying Article 250 [630.15].
     
  9. Resistance welders have special requirements above and beyond those for other welders. These are detailed in Article 630, Part III.
     
  10. Welding cables have special requirements, and these are detailed in Article 630, Part IV.