Sharing a 240v Circuit

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  #1  
Old 01-06-06, 12:50 PM
KDYMANIAC
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Sharing a 240v Circuit

I have an existing 240v 40A circuit dedicated to a free-standing range/oven combo that gets very little use. I would like to share this circuit with a newly acquired tanning bed. The tanning bed requires a 230v 30A power supply. I have a buck/booster transformer to step down the voltage. Could I have a junction box installed and extend the circuit to the location of the tanning bed (approx 6 feet)? Are there NEC issues with such a plan?
 
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Old 01-06-06, 02:13 PM
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The voltage would be OK, 230 & 240V equipment (listed in the USA) are for installation on similar type circuits.
If the tanning bed instructions indicate 30A max circuit breaker (or fuse), then the 40A circuit wouldn't work unless you installed a local 30A breaker (or fuse) to reduce the circuits ampacity.
Another fly in the ointment may be if the oven is hard wired, and is rated at more than 50% of the circuit (50% of 40A is 20A), no other receptacles can share the circuit [see 210.23(A)(2) in your NEC].
 
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Old 01-06-06, 02:15 PM
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You don't need the buck & boost transformer. Typical home/shop loads listed from 220-240V are pretty much the same and all will work from 240V circuits.

Typical Miller welding machines are listed as 230V. Virtually all are used on 240V.

However, you really need dedicated circuits for any 240V loads.

That said, yes, it is certainly doable safely, just not to Code.
 
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Old 01-06-06, 02:15 PM
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Originally Posted by KDYMANIAC
I have an existing 240v 40A circuit dedicated to a free-standing range/oven combo that gets very little use. I would like to share this circuit with a newly acquired tanning bed. The tanning bed requires a 230v 30A power supply.
This would not be allowed for several reasons, the most important is that the range requires a 40A breaker, and the tanning bed requires a 30A breaker. The two cannot coexist on the same circuit, because they require different levels of overcurrent protection.

I have a buck/booster transformer to step down the voltage.
That would be unneeded. In the US and Canada the words 220V, 230V, 240V and 250V all mean the same thing. The power company supplies your house with a voltage somewhere in the range of 220V - 254V; appliances are designed to handle this range.

Could I have a junction box installed and extend the circuit to the location of the tanning bed (approx 6 feet)? Are there NEC issues with such a plan?
Unless this range circuit is newer than 1996, there is another reason you cannot extend it. Most range circuits installed prior to 1996 were ungrounded 3 wire; today's code requires a 4 wire grounded circuit. It is against code to extend an ungrounded circuit.

Because of the large current draw of the tanning bed, it is not considered general-purpose equipment. Therefore, it must have a dedicated circuit designed and installed to meet the bed's specifications.
 
  #5  
Old 01-06-06, 02:39 PM
KDYMANIAC
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A couple of followup questions:

The range line was installed after 1996 and has two hot one neutral and a ground. However, the service panel has a single bar for neutral and ground wires returning to the panel. Is it normal to have the neutral and ground wires share the same bar in the service panel?

Could the ampicity issues be solved by having a small service panel or fused disconnect installed downstream from the range with 30 amp protection?

As for the general-purpose equipment/large draw issue, I guess I will have to have a new circuit installed...or is there a way I could have the circuit split with a switch between the two devices to isolate power to one or the other leg of the circuit?
 
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Old 01-06-06, 02:45 PM
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Originally Posted by KDYMANIAC
Is it normal to have the neutral and ground wires share the same bar in the service panel?...

As for the general-purpose equipment/large draw issue, I guess I will have to have a new circuit installed...or is there a way I could have the circuit split with a switch between the two devices to isolate power to one or the other leg of the circuit?
Yes, they are required to be bonded (or the same) at the service.

The switch/extra fuse (essentially trying to mickey mouse a subpanel) would be more trouble/time than running a new circuit from the panel, all things considered.
 
  #7  
Old 01-06-06, 11:13 PM
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Originally Posted by MAC702
That said, yes, it is certainly doable safely, just not to Code.

The purpose of the NEC is; “the practical safeguarding of persons and property from hazards arising from the use of electricity.”


I realize you probably follow a different set of rules, but to suggest it is safe to disregard the NEC is irresponsible.
 
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Old 01-07-06, 05:45 AM
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Ug. This starts getting into issues of the philosophy of the code.

To answer the OP: you could do this, and you could do this safely, but it would require much more effort than simply running a new line.

You would need some sort of interlock switch that would permit only one load to be used at a time, and you would need a disconnect box with a suitable breaker for the lower amperage load. You might be able to do this with a subpanel, using the current line as a feeder to a subpanel, and then you would need to install switch rated breakers in the sub panel, and then interlock the breakers so that only one was on at a time. You need the disconnect box or subpanel because the loads require different breakers, and you need the interlock because the feeder circuit is not sufficient to handle both loads at the same time. There are probably numerous details of how to do this that I've not mentioned.

As far as something being 'safe but not to code', there are several possibilities.

1) Safety is really a game of chance. Even code compliant installs have some risk. You could put in a system that is not as safe as a proper code compliant install, but it would still be pretty safe. For example you could install a three wire range circuit rather than a four wire circuit. This was 'safe enough' for previous versions of the code, and still pretty darn safe, but not as safe the experience of the code writing panel has determined is necessary.

2) Testing. Code requires that certain components be 'listed', meaning tested and approved for the use by a testing lab, eg. UL. Without the test, the apparatus might be perfectly safe, but you don't have proof of this fact. The place where you will encounter this is when you wish to use foreign equipment; it has been tested as safe to the standards in the other country, and is probably pretty safe, but there are enough differences in assumptions and electrical system practise that you really need testing to NEC standards.

3) Labeling. Many components are required to be labeled appropriately. An example is wire. Wire that is essentially the same, but without the label, is essentially safe, but not to code. Where might you find this? Wires inside of cable assemblies are generally not labeled, since the entire assembly carries the label. Wires stripped out of a cable assembly and used in conduit are safe but not to code.

4) Wishful thinking. The code is an imperfect product of years of experience. As equipment develops and failures are investigated, code changes. The use of grounding, the '42 circuit rule', the requirements that splices be in junction boxes, etc. are all the result of experience with failures. Sometimes someone will get a bright idea, and then without testing, claim that 'this is better than code', all without any testing or experience. Very often 'safe but not code' is wishful thinking on the 'safe' part.

*grin*

Just run the new circuit; then come back here and we can discuss how many angels can dance on the head of a pin.

-Jon
 
  #9  
Old 01-07-06, 07:44 AM
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Articles 210.23, A thru D, apply to "A Branch-Circuit supplying two or more outlets (loads)."

210.23 (A),2 applies to 15 and 20 amp B-C's

In dwelllings, a 40 amp B-C with two or more loads is restricted to cooking appliances. ---- 210.23 (C)

210.23 (B), 30 amp B-C's, permitts two or more loads on a 30 amp B-C for "utilization equiptment in any occupancy". This presumes that the circuit complies with the the "basic rule" of 210.23------ "In no case shall the load(s) exceed the B-C rating ( in amps)"
 
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Old 01-07-06, 08:18 AM
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On the first one I wired I called about the voltage issue of 230 vs 240. The rep said that not using the buck boost would shorten the life of the bulbs.
 
  #11  
Old 01-07-06, 08:57 PM
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Originally Posted by Juhl
The purpose of the NEC is; “the practical safeguarding of persons and property from hazards arising from the use of electricity.”

I realize you probably follow a different set of rules, but to suggest it is safe to disregard the NEC is irresponsible.
Eh? I'm not sure what you are implying here.

To state that ONLY Code-approved installations are SAFE is absurd. I follow the Code, but I also recognize the simple fact that LOTS of perfectly safe installations are done everyday that would not pass some technicality in the Code.

It is certainly possible to have something completely safe that also is not done to Code.

My statement that it was POSSIBLE to do it safely, though not to Code, is correct. There's plenty of UNSAFE advice here to worry about; THAT is what is irresponsible. Have a little more discernment in whom you call irresponsible, please.

Example: I build my own house. I don't want a receptacle behind the door in my bedroom, because that would be, well, STUPID. But since there is a closet on that entire wall just past the door, I am required by the Code to put a receptacle behind the door in my bedroom. If I choose NOT to, it violates the Code. I guess it is therefore UNSAFE and IRRESPONSIBLE to not want to put it there.

I realize the OP had different issues, and I certainly did not suggest it would be EASY to do it safely, by the Code or otherwise.
 
  #12  
Old 01-07-06, 09:00 PM
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Originally Posted by pcboss
On the first one I wired I called about the voltage issue of 230 vs 240. The rep said that not using the buck boost would shorten the life of the bulbs.
What is the voltage rating that is actually listed on the bulbs? NOT the one listed on the label of the tanning bed...
 
  #13  
Old 01-08-06, 10:15 AM
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The code is based on safety, and nothing except safety.

There are hazards that are obvious to us, and hazards that are not. Usually, when we say that something is safe but not to code, it only means that we don't have enough experience to see the risk And we are most vulnerable to risks we can't see.

Having said that, not all risks are the same. Risks associated with some code violations are so slight that even inspectors grant variances to the code in certain situations.

Nevertheless, it's a dangerous road to travel to think that the code is a bunch of technicalities that have no bearing on safety. Only people with vast electrical experience should grant themselves the luxury of deciding when violating the code is a worthwhile tradeoff.
 
  #14  
Old 01-08-06, 04:50 PM
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The OP asked if a 40 amp circuit serving a cooking appliance could be extended to also serve a 30 amp load. The answer is no. It would violate a number of codes, would not be safe and depending on local jurisdiction, would be illegal.
Mac simply stated it was safe to extend this circuit. It is not.
The suggestion Jon offered did not involve extending the circuit, but adding a questionable? sub panel with a transfer switch set up.

I agree that safety is relative, we make decisions weighing risk and consequence all the time. Here, we are talking about something that has the potential to kill when safety measures are disregarded.

Mac, I did not call you irresponsible. My point was, suggesting it is ok to disregard safety measures, especially with something as potentially dangerous as electricity, is irresponsible. I’m sure we have all done something irresponsible at some time. If a person frequently acts irresponsibly then I suppose that would be an irresponsible person.

I am reminded of other arguments I’ve heard:

From someone smoking while pumping gas. “Its ok I work at a gas station.”

From someone thinking smoking is not harmful. “My grandpa smoked 3 packs a day since he was 10 years old and lived to be 104.”

From someone who can’t quit smoking. “You gotta die from something.”
 
  #15  
Old 01-09-06, 06:29 AM
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A neutral is a current carrying grounded conductor!
 
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