Branch Circuit and OCPD Selection for Fork Lift Battery Charger

[h1h2h3]

Hi All,

Got a call to wire a 3 phase 208v battery charger for a fork lift and I have to say I'm a bit confused by the MF specs and requirements. I also have a couple questions regarding the NEC requirements for this installation.

This is a 3 phase 3 wire converter, factory wired and fused for 480v, field convertible to 208y. Nameplate specs: AC input: E: 208/240/480 I: 20/18/15 Ph: 3 Hz: 60 DC output: E: 36 I: 129. Inside of the cabinet there is another sticker that states that the DC fuse is 200A and that the AC fuses are to be 35/30/15 respectively (these fuses are an integral piece of the equipment (ie: fuse blocks mounted within the cabinet). The instruction manual reflects the same information as the sticker inside of the cabinet. Now I have never installed one of these, so I am unfamiliar with the requirements, however, there seems to be a disconnect in this information. I am wondering why there is OCPD (line side of the charger) at 175% of nameplate current. I contacted the MF who confirmed that this information is in fact correct, however, they could not specify why :rant:. Further, they would not confirm the branch circuit selection which I would assume would be a 3 pole 40 amp 208 volt breaker, wired to an un-fused 3p 60A safty switch (disco) using 8awg Cu conductors (90 deg rated as my method will be mc to emt). I just don't see in the NEC why the need for a line this size if each leg is only pulling 20 amps at 208. The articles I've checked are 511.10(A), 625 (although this article does not include forklifts), 480, and even 450 only because it looks like a transformer.

FYI this equipment is provided with an internal shunt (dc side) and I believe an internal interlock. It is listed to be floor mounted with mounting restrictions made for ventilation clearances. I was also wondering if this needs to be bonded to building steel, I know it may sound like a ridiculous question, but it looks identical to a transformer, which I understand is never a good reason to do anything, but it peaked my curiosity and I'm not too proud to ask. Or, is the EGC a suitable means of bonding to the system?

If anyone else is familiar with these installations I would really appreciate any installation tips/pointers you might have as well as code articles specific to this type of install.

Thank you all for your time.

 

[iwire]

Never mind

 

[h1h2h3]

Never mind

nevermind what? did i break a forum rule?

 

[iwire]

nevermind what? did i break a forum rule?

No, not at all.

I posted something stupid and changed my mind.

 

[Smart $]

Could be to handle inrush on power up. It'll be similar to a transformer.

A 36V DC system is not required to be grounded, so there is no Code requirement to bond to building steel.

 

[h1h2h3]

Could be to handle inrush on power up. It'll be similar to a transformer.

A 36V DC system is not required to be grounded, so there is no Code requirement to bond to building steel.

So would I be correct in my branch circuit selection of #8 to a 40 A OCPD or should I base my breaker and wire size on the continuous load (Ix125%). Which in this case is 20?1.25=24 so #10 on a 30. Doesn't seem right protecting it at the charger with a 35 and then at the panel with a 30. I would think that on inrush it would then trip my breaker first.

 

[Smart $]

So would I be correct in my branch circuit selection of #8 to a 40 A OCPD or should I base my breaker and wire size on the continuous load (Ix125%). Which in this case is 20?1.25=24 so #10 on a 30. Doesn't seem right protecting it at the charger with a 35 and then at the panel with a 30. I would think that on inrush it would then trip my breaker first.

There is nothing in the Code which prevents you from putting it on a 40A circuit AFAIK. I ? 125% is just the minimum, and only if continuous... it may not be, as current will probably drop off as the battery charges.

You could possibly get away with a 30A circuit. Typical breakers are inverse-time acting. You'd have to know the inrush and drop off and compare to the time response curve of the breaker if you wanted to ascertain no nuisance tripping before installation.

 

[h1h2h3]

So it sounds to me like I originally thougMF that that 40 Amo circuit is the way to go to insure a safe nuisance free install. I doubt I will get the inrush I info from MF because they just regurgitate the data sheet back to me. I'd rather overkill it a bit then run the risk of an inferior install. I know that with loads that are all "transformer" like this one, things can get weird and wrong real quick.