Is there any need to run 3 wires (plus ground) for my shop 200v outlets or is 2 wires sufficient? Another way of putting it, is there any machine or potential use that may require 3 wires?
[OP]
Contributor
Is there any need to run 3 wires (plus ground) for my shop 200v outlets or is 2 wires sufficient? Another way of putting it, is there any machine or potential use that may require 3 wires?
Member
220V is line to line. Line to ground is 110V. So unless the 220V appliance also has a 110 circuit (i.e. stoves, dryers) you only need the two line wires (and a ground). That is at least true where I live. I paid an electrician to run wires for a recent addition but did the finish myself. I didn't know when I agreed to do it that meant hooking up the two 220V circuits to the heat pump but I managed. Both were just two insulated wires and a ground. Air handler was 8 gauge and condenser was 10 gauge (it's a 2 ton unit). No manual or other instructions were available but the devices had little diagrams on them.
Member
I had a table saw that needed 120/240 because the starter had a 120 relay. I replaced the relay.
Other than that I have never seen a shop tool that required both.
Contributor
The shop in the house I recently bought was already wired 3 wire plus a ground. I decided that was fine by me because, if I ever needed it that way, I didn't have to rip stuff up to change it later.
Member
I have one 30A outlet that is configured for both neutral and ground - just in case. The rest just include both hot legs and ground. The only 240VAC shop equipment I have seen that required a neutral connection was a 5 hp drum sander that had a small 120VAC motor just for the variable feed mechanism.
Contributor
I've found it very convenient and worth the small cost of the extra wire to use a 3 wire "multi wire branch circuit" for all of my non-dedicated circuits (I know others here disagree, fairly vehemently). At most locations I put in a quad 120 V outlet, with each pair on a different circuit and one or two 240 V outlets. Many of my tools have accessories (e.g. a lamp) that wants 120 V, while almost all the tools are 240 V. For dedicated large draw tools (e.g. dust collector, compressor, table saw) they get a 2 wire 240 V circuit. It's easy to reconfigure this setup as needs change.
I've never run across a power tool wired to require both 120 and 240, tools that need it that I've seen, like my sander, have two plugs, one 240 V for the sander motor, a second 120V for the feeder.
Member
Yes.Originally Posted by Steve Mathews
If you are wiring for specific machinery, you need to have the manufacturers specs on wiring requirements and outlet (NEMA) configuration. If you're wiring for whatever you may need, pull a neutral in with each 240V pair. (The majority of homes run on 120-240v. 110-220 is obsolete.) If you're running pre-wired cabling (Romex, BX, etc.) use 4-wire cabling. The difficult question to answer is what gauge wire to pull? At a minimum, in a workshop, you should be running #12 (gauge) wire. But you may need #10 (typically 30 amp loads) or larger, depending on the load. So it's always good to configure your anticipated machinery and load demands before wiring your shop, and plan for the future when doing so.
Member
It's line to neutral, not line to ground which gives you 110 or 120V.
Member
It's either. Anytime you want to check the voltage of a current carrying conductor, you should first check it to ground. If you can't find a ground close enough, you then check it to a neutral you know is good. When a transformer is tapped to split 240v into 120v, the center tap becomes the neutral and either hot leg to neutral will read 120v. Often, the neutral is bonded at the service entrance creating direct continuity between ground and neutral. But even if the neutral is isolated, you will still get a full voltage reading from any hot leg to ground or neutral.
Member
I stand corrected, didn't read Jim Dwight's post thoroughly, one leg to ground will read 120V on a meter, if you need 120V for a timer or a lamp etc.. in addition to the 240V for the motor or appliance, which Jim stated, you do need to go use one leg and a neutral. Sorry, I just wanted to make sure that someone didn't think that it was OK to use a hot leg and the ground to pick up an auxiliary 120V.
Member
Your main panel in the shop will almost certainly have two hots and a neutral feeding it, so you can run both 120 V and 240 V equipment in the building. I believe it is code as well to have to run a neutral to the panel as well with standard 240 V single (split) phase. Nearly all 240 V shop equipment is 240 V only and you will just need to run two hots and a ground to them. For typical shop equipment a 3 hp motor will need a 12/2 wire with a 20 A breaker and a 5 hp motor will need a 10/2 wire with a 30 A breaker. You do have to tag the white wire at both ends with a piece of electrical tape or mark it with a marker to indicate it is actually a hot rather than a neutral.
Anything over 20 amps has to be on a dedicated circuit but in most places you can have more than one 20 amp/240 V receptacle on a branch. You just need to be careful there as you may exceed 20 amps by having two tools running on the same circuit at the same time.
Last edited by Phillip Gregory; 03-04-2015 at 10:59 PM.
Member
Per the NEC the ground is bonded to the neutral at the service entrance only. Your neutral should not be bonded to the ground if your shop's panel is a subpanel but it must be if your shop's panel comes straight off the meter and is a separate service entrance. You may not get a correct hot to neutral reading if there is some gross imbalance between the two 120 V legs occurring somewhere causing a significant neutral current. That would be a separate problem in itself though...
Member
There are situations where the neutral is bonded past the service entrance. I've never seen it in residential applications but I have seen it in commercial and industrial applications. The NEC is the starting point for how things should be put together but doesn't cover every situation and is sometimes behind the times. But if one is concerned about passing inspection, one will always get the right answer to every installation question if you ask your local inspector. And don't be surprised if his or her answer is different than the NEC.
Buck, you are right about not using a ground to complete a load circuit. I was talking only about checking voltage with a meter and hope I wasn't giving the impression a ground is an acceptable neutral. As for funky neutrals, they certainly exist and they can be a nightmare to trace out. That's why I stated "check it to a neutral you know is good." Anyone checking voltage should never assume the neutral is good for doing that. That's why we (electricians) always start with a ground when getting a voltage reading with a meter. Of course, you have to know the ground is good too. Same goes for whatever meter you are using. Check, check and double check everything. It's a process drilled into our heads from day one. And sometimes the failure to verify everything is as you assume it to be drills it in even further.
Member
The Authority Having Jurisdiction can certainly (and often does) make up their own rules. What they say is what you have to do, or you fail the inspection. Many places out in the sticks like where I live don't have any permitting or inspections so the NEC is the default for what you do.
No woodworking machine that you will use. Appliances, such as range and most dryers now require 4 wire 240 circuits. But If it were me, (and I ran my last shop this way) is to run 3 wire.
Posting Permissions
Reply With Quote