well, it is really interesting
Guest
well, it is really interesting
Contributor
Originally Posted by Art Mann
Not prohibited by the NEC, but is prohibited by the IRC.
Moderator
I give up, what's IRC?
Internet Relay Chat?
International Rescue Committee?
Member
Dave,
I would not run my shop on this setup.
I agree totally with what Charles said and give an example why I think he is right. I recently had an experience with my bandsaw motor (2 1/2HP) that it was make a lot of noise & tripping the breaker. The motor shop determined the field was bad and it was shorting out internally (or something like that). What if that motor had been on a 50A circuit? I think there might have been some smoke involved?
It is not that difficult to put in a subpanel and run individual circuits. This is especially important on your 110V circuits which can easily become overloaded just by turning on a shop vac.
All my ww'ing machines are fed by one 240V circuit #12 wire/20A. My DC is 110 on a dedicated circuit.
When I expanded my shop, I had a separate service put in and had to hire a licensed electrician to do the work. I thought I knew a lot about wiring, but boy did I learn a lot.
Member
Agree with Charles. over current protection for the win. I run several machines (lathe, Unsiaw, Powermatic band saw) off of VFD's...thinking of putting fusible protection in front of (line side of ) VFD's for additional protection.
Contributor
A 240 volt machine should really have overloads or a VFD supplying it. A VFD is rated as an overload and I believe most are rated as a service disconnect. This makes the cost of a VFD seem not so high compared to a proper code installation with a high amp disconnect switch or at least a plug and receptacle. And I think a 240V machine with moving parts really should have a contactor so it turns off if the power goes out.
Add it up, a 240 motor starter with overloads, and a separate switch is going to be around $50-150 used
Bill D
Member
I ran the equivalent amount of loads in my shop without any issues. I had a 5hp PM66, 5hp Clearvue, overhead air filter, and lights at the same time. Never blew the breaker. Start the dust collector and let it come up to speed before starting the saw. If possible, try to run a separate line for the lights so you are not standing there in the dark if the breaker does trip.
This assumes that the 50A breaker feeds a sub-panel with appropriate sized sub circuits.
Steve
Member
Are you sure about this, Charley? Does this only apply to circuits above 20 amps? There is no way my LCD TV, or many other, power cord is rated to handle 20 amps (the size of the breaker wired with 12g wire). It was my understanding the breaker protects the "in wall" wiring between the breaker and up to and including the outlet. The protection for the machine is provided at the machine. Most, if not all, of my machines have protection just after or before the power switch. Thus the only item at risk for the situation you describe is the power cord between the outlet and the machine's power switch.
Moderator
Anthony, the wire rating Charles is speaking about is primarily about the actual circuit...the "wire in the wall" must be rate to be at least the minimum for the circuit's breaker rating. If you're putting in a 30 amp 240v circuit, for example, you'll use a 30 amp breaker, 10 gage minimum conductors "in the wall" and 30 amp rated terminations at the other end, presumably a 30 amp twist lock recepticle. (the circuit could conceivably terminate directly on the machine, but it's a best practice to have a positive disconnect which is usually either a plug or a disconnect switch)
What you plug in at the other end is a different situation entirely. "Appliances" like TVs, mixers, Microwaves, etc., all presumably have a cord that's acceptable for their needs. In our woodworking world, the slight difference is that we often need to provide the cord for the machine and when we do so, we should provide a cord and terminations that are appropriately rated for the motor(s) involved. Many of our woodworking machines do have some level of "local protection" for overloads; sometimes on the motor itself, and sometimes in the circuitry. (My MiniMax slider has multiple breakers inside the control panel)
--
The most expensive tool is the one you buy "cheaply" and often...
Moderator
Well, the statement that also caused me to do a double take apparently referred to both the tool and the cord connecting the tool to the building wiring:
" You are doing exactly that when you connect a tool that only requires 20 amps and is only wired with wire that can carry 20 amps safely. If a short circuit occurred in that tool or wire and the 50 amp breaker was directly feeding it, there would be flaming power cords and power tool long before that 50 amp circuit breaker tripped."
While I agree that matching the tool to the breaker may be a good idea I don't remember seeing that in the code (although it has been a long time since I studied the code.) That said, I do like to size my breakers to the use for dedicated tools, even if it takes putting in a sub panel with smaller breakers. But I can't know if a 20 amp breaker will trip before a 5-amp tool on a 16 gauge plug-in cord causes a fire due to an overload or short.
JKJ
Moderator
Well, the concern is valid, for sure, John, although one would hope that as soon as "conductors merged" after getting toasty, the short circuit would hopefully pop the breaker. That might not happen, however, and plenty of fires have occurred because of malfunctioning equipment and/or cords attached between that equipment and the circuit. The code can only really address the building infrastructure, however, given the "stuff" connected to the circuits over time may vary, but the circuits, themselves, are "permanent".
--
The most expensive tool is the one you buy "cheaply" and often...
Contributor
Maybe our British members can chime in here. I understand that in Britain it is common to supply outlets with parallel wires fed from both ends. This means you can trip one breaker and the other one will keep the outlet powered.
The net effect is that each cord end has an internal fuse sized for that appliances power needs.
In the USA I only see this on Christmas lights.
Bill
Contributor
That doesn't seem to make a lot of sense, if I understand what you're proposing. Let's skinny it down to make it easier to understand. Let's say you had one outlet, and you had that outlet supplied by two breakers and two sets of wire, and let's say each breaker was 20 amps. In essence you have an outlet that is "protected" with 40 amps of breaker because each breaker would supply about the half the current.
If there was an imbalance, let's say at the limit, one was trying to supply 21 amps and the other 19 amps, the first would trip and then the second would immediately trip because the 40 amps would try to come through that remaining breaker.
Mike
Go into the world and do well. But more importantly, go into the world and do good.
Member
What you're describing sound a lot like a Ring Main, except a Ring Main only has one breaker. Both ends of the ring terminate on the same breaker.
Last edited by David L Morse; 12-30-2017 at 9:20 AM.
Beranek's Law:
It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker. In this case, the frequency response of the loudspeaker seems to play only a minor part in forming a person's opinion.
L.L. Beranek, Acoustics (McGraw-Hill, New York, 1954), p.208.
Contributor
think you are right. the term "ring main" sounds familar. I knew it was different then USA code. I guess one breaker makes a lot more sense. It does save on wire. Was this method used before the war or did it come during/after to reduce wire needed for the war effort?
I
Posting Permissions
Reply With Quote