Derating Quandary

[Smart $]

One of the reasons for the separate breakers for the welder/plasma (#1) & mill/lathe (#3) was because my understanding is that 230VAC loads each require their own means of disconnect. Is that correct?

In the general sense, no. But many line-to-line equipment fall under the more specific Articles which may place such limitations on these circuits.

If so, then is a plug and receptacle considered a "disconnect"?

In many cases, yes. But then we get into the more specific Articles and it could be no. Even in the general sense, 110.58 requires a transformer (most welders are, in a sense, enhanced transformers) or motor (which I'm certain the mill/lathe has at least one ) to have a switch or circuit breaker as the disconnecting means.

(Note: These are not large industrial machines, so I think a fused-disconnect is overkill. Unless that is a requirement for them to be on the same branch.)

The fused disconnect I mentioned is because the only way the 30A circuit can be considered a feeder is if you tap off it*, which will require the tap conductor to be smaller than the feeder (if the same size it would not be a tap). Tap rules require termination of the tap conductor's load end to a single ocpd (the fused disconnect)

* As others have stated, another option is to feed a subpanel.

 

[Jon456]

The fused disconnect I mentioned is because the only way the 30A circuit can be considered a feeder is if you tap off it*, which will require the tap conductor to be smaller than the feeder (if the same size it would not be a tap). Tap rules require termination of the tap conductor's load end to a single ocpd (the fused disconnect).

But could both circuits #1 and #3 be merged as a single 30A circuit with #10 or #8 wire (so not a feeder & tap)? And could the outlet(s) for the mill/lathe be 20A receptacles (in the same way that 15A receptacles are commonly used on 20A 115VAC circuits)?

But I suspect this statement of yours will kibosh the whole idea:

Even in the general sense, 110.58 requires a transformer (most welders are, in a sense, enhanced transformers) or motor (which I'm certain the mill/lathe has at least one ) to have a switch or circuit breaker as the disconnecting means.

The question is: must they EACH have their own switch or circuit breaker? I suspect that may be the case. :|

So I think I'm back to separate conduit for the isolated ground branch.

 

[e57]

But could both circuits #1 and #3 be merged as a single 30A circuit with #10 or #8 wire (so not a feeder & tap)? And could the outlet(s) for the mill/lathe be 20A receptacles (in the same way that 15A receptacles are commonly used on 20A 115VAC circuits)?

But I suspect this statement of yours will kibosh the whole idea:



The question is: must they EACH have their own switch or circuit breaker? I suspect that may be the case. :|

So I think I'm back to separate conduit for the isolated ground branch.

It would make more sense for 2&3 to be together for OCP reasons - depending on the actual load of each they could share a set of recepticals as disconnect - but I doubt this is what your client is looking for in the long run. While both may require 30A for starting, the load on each may be much lower. Niether is continuous, and one is intermitant at best.

So why is it you are fixated on one conduit only? Is it there already? Besides the conduit - box fill on the other end is something to think about...

 

[Smart $]

But could both circuits #1 and #3 be merged as a single 30A circuit with #10 or #8 wire (so not a feeder & tap)? And could the outlet(s) for the mill/lathe be 20A receptacles (in the same way that 15A receptacles are commonly used on 20A 115VAC circuits)?

Well the circuits could be merged, but you cannot put a 20A-rated receptacle on a 30A circuit... any receptacle would have to be 30A-rated. Would need more details on mill/lathe (minimally, the nameplate data). It's a little much for equipment you say will draw 15A max, but it could very well be possible being there is one or more motors involved.

But I suspect this statement of yours will kibosh the whole idea:

The question is: must they EACH have their own switch or circuit breaker? I suspect that may be the case. :|

I can't think of any requirement which specifically states they must be on individual disconnects.

If the 30A circuit terminates to two 30A-rated receptacles, this gets into a gray area in the code in that until something is plugged into these receptacles, it is simply a multi-outlet receptacle circuit. Even thereafter, the code has little control over plug-and-cord-connected equipment.

So I think I'm back to separate conduit for the isolated ground branch.

Can't advise you one way or the other here....

 

[e57]

Lets put this into perspective - you want to stuff 8 breaker spaces through one puny 3/4" conduit - to an area that could very well need more down the line.

3 - #6 and a #12 IGC could go through EMT as the ECG for the rest, could cover all of it in a 12 space panel...

I don't understand why? Unless solely for the exercise of derateing... That said - you may or may not would need to up-size conductors, and may have to up-size conduit to 1"~1-1/4" - depending on connected load. (Not the OCP size)

Or get creative by joining circuits - which is another exercise it seems has it's issues that we seem to have already seen...

 

[Jon456]

It would make more sense for 2&3 to be together for OCP reasons - depending on the actual load of each they could share a set of recepticals as disconnect

The problem with that is the compressor could (and probably will) come on while the mill or lathe is running. In which case I'd have to size that circuit for at least 30A anyway. And even then I think that scenario would be less than ideal.

but I doubt this is what your client is looking for in the long run.

Ok, I'll confess... I am my own client for this job. I recently moved and I need to upgrade the wiring in my garage for my machinery (currently, there is but a single 115V/15A outlet). I am trying to keep the costs down as I have no other client to bill for this project (and with the economy being what it is, I'm not exactly rolling in cash).

As for future-proofing, I've already factored that into the design. All the circuit ampacities were set with the idea that machines could be upgraded in the future. I doubt there will ever be more heavy machines added simply because there will not be much additional space available along that wall. But if another machine could be squeezed in, it could share the mill/lathe circuit which has extra capacity. Besides, no more than one machine will ever be in use at the same time.

 

[e57]

Ok, I'll confess... I am my own client for this job. I recently moved and I need to upgrade the wiring in my garage for my machinery (currently, there is but a single 115V/15A outlet). I am trying to keep the costs down as I have no other client to bill for this project (and with the economy being what it is, I'm not exactly rolling in cash).

AHHHHH the truth!!!!!

I'm still gonna say - the same - a panel - but in your case - a used one... or at least used CBs and a few KO seals... on boxes and some recycled wire. I understand - and am home on my rear... ( I also just lost a 1 1/2 tube steel running for a phone call - no idea where I left it... :roll These posts actually reminded me I had a little unfinished project to stave off boredom.

Take a look at the two 2P 30 loads - the actual HP/and FLA - try them out together lathe running under load, with the compressor kicking on. IMO there is little chance it will trip, and if the load itself is under 7200VA - go for it.

Some shop talk though - I have a Lincoln 175+ on a two wheeled hand-truck with a full sized tank, and a panel screwed to it. The panel is a CH 12/24 with 2 GFI's and a CA 50 cord whip as a feeder - I can take it outside - anywhere in my garage... and it has a cord for my grinder and bandsaw right there... Packs up nice and can be stuffed in a corner. If I put the 100' 8/3w/g on it - I can bring it up hill/steps to my back-yard... If you get funds for doing it down the line - do it.... Everything in my tiny shop is on wheels...

The other stuff - still a panel.... It is the easiest - most flexible - economical bet... 2P50a on #6 in 3/4 and an enclosure on the other end - add in as required or as funds allow.

 

[juptonstone]

Because the neutral carries a return current, I believe that it too is considered a current carrying conductor... so you really have 12 0r 13 current carrying conductors. It seems to me that you'll need to derate the wiring so much that it would be far easier to run two separate sections of conduit with 6/7 current carrying conductors each. I havent done the fill calcuations, but I'd guess 2 - 3/4" EMTs would do the job.

 

[Smart $]

Because the neutral carries a return current, I believe that it too is considered a current carrying conductor... so you really have 12 0r 13 current carrying conductors. ...

Agree with the first part of your statement, because there are two two-wire circuits with neutral conductors, but I do not agree with the second part...

5 circuits ? 2 wires each = 10 current-carrying conductors (ccc's).

Where'd you come up with 12 or 13??? The only way I could see is either you are counting the EGC's, or thinking the line-to-line loads are 3?. EGC's are never counted as ccc's, and the OPer's system is 120/240 1? 3W.

 

[e57]

and the OPer's system is 120/240 1? 3W.

There is a small possiblity that it is not... Many townhouse type complexes and other non-free-standing residential may be 120/208 1? 3W from a 3? 4W service.... We also don't know something else... If this is a free-standing garage or not????? Which is a game changer! We also still don't know what the fixation is to 3/4" EMT for the application - location of the panel feeding this - or the actual loads to be connected... There is still quite an un-clear picture.

Otherwise 310.15B4 tells us which neutral is a CCC.

 

[dmagyar]

Add a sub panel, avoid the problem

Add a sub panel, avoid the problem

Not to be a S.A. but why not install a sub panel in the garage. Then all the feeds originate there and you have a smaller conduit to the garage from the main panel.

 

[Smart $]

There is a small possiblity that it is not... Many townhouse type complexes and other non-free-standing residential may be 120/208 1? 3W from a 3? 4W service.... We also don't know something else... If this is a free-standing garage or not????? Which is a game changer! We also still don't know what the fixation is to 3/4" EMT for the application - location of the panel feeding this - or the actual loads to be connected... There is still quite an un-clear picture.

Otherwise 310.15B4 tells us which neutral is a CCC.

Hmm... good points!

However, even a 120/208 1? 3W service would mean 10 ccc's.

Yet, it is good that you make these points (I do at times myself). Many times the poster doesn't realize or state the "null and voiding" information

 

[Smart $]

Not to be a S.A. but why not install a sub panel in the garage. Then all the feeds originate there and you have a smaller conduit to the garage from the main panel.

Cost seems to be the reason... but I'm certainly not going to do a cost analysis for him.

 

[e57]

Cost seems to be the reason... but I'm certainly not going to do a cost analysis for him.

Nor was I - But IMO it be worth it to do one.

 

[e57]

However, even a 120/208 1? 3W service would mean 10 ccc's.

In this situation yes... But any neutral would count on 3 wire circuits if any...

 

[e57]

FWIW this is my rig...

(Welcome to my mess...)

The panel on the hand cart serves the welder and the cord wrapped around it - sure wiring a cord into a panel is a violation - but I'm comfortable with it.... And the welder itself is a violation of workspace - only if it is plugged in IMO... OH - and that is my other garage panel back there that feeds this on (when it's plugged in.) and ahhhh yes it has a workspace violation too... But I can move that old van seat with ease....

 

[LarryFine]

But I can move that old van seat with ease....

Looks like the middle bench from a Dodge Caravan or Plymouth Voyager.

 

[e57]

Looks like the middle bench from a Dodge Caravan or Plymouth Voyager.

'86 Astro - long since gone. It's mounted to a peice of plywood - and makes a good place to take off muddy boots. It has also been to burning man twice and some other car camping experiances... The panel behind it next to the stairs is is mounted on floor to cieling strut. Since there is little wall space available in there.