240v to Espresso cart using two 120 V out;lets

[rcwilson]

A portable espresso cart operator sets up his cart at our church carnival and other events in our area. His espresso machine has a 230V, 30A twist-lock plug on a heavy power cord. But few facilities have 230V twist-lock receptacles so he uses two long 120 V extension cords wired in a cheater cord with a single 230V female plug. He runs around with the two cords and a meter until he finds two outlets that give 208 or 240 V at his plug. He doesn?t bother checking to see if the outlets are on the same multi-wire circuit or even the same panel.

This is the third espresso cart operator I have seen doing this. They all claim that it is no problem because the breakers don?t trip and they have never had a problem and ?we do it almost every day at the Microsoft complex.? One cart operator uses a metal j-box with a panel voltmeter in the cover to help identify the ?proper circuits.? He tries different outlets until the meter?s needle goes into the green zone.

After one event we had to rewire several outlets which had melted wiring, but we couldn?t identify if it was due to the illegal espresso tap or because the kitchen ladies had plugged in ten food warmers.

What codes are they violating? How bad of a safety issue is this? The load appears to be about 2000 watts or less than 10 Amps. (He wouldn?t let me look at the nameplate.) Any ideas how to stop these guys from burning up more wiring?

 

[petersonra]

Re: 240v to Espresso cart using two 120 V out;lets

if you had melted wiring it was not because of this guy. if you had to much current flowing the overcurrent protection device9s) should have tripped. if they did not, you have a premises wiring problem.

I don't see how what they are doing is a safety hazard.

 

[charlie b]

Re: 240v to Espresso cart using two 120 V out;lets

I think this is a violation of 400.7(B). When an appliance is supplied by a flexible cord, the cord is required to become energized only when plugged into a (count them, "one," as in "singular") receptacle.

As to the hazards, I see two:

First, suppose the two receptacle outlets are from the same panel. Suppose a maintenance worker wants to replace a different receptacle that is powered from one of the two breakers that supply the two receptacles into which the espresso machine is plugged. At the moment, the espresso machine is idle ? drawing no current. The maintenance worker turns off the appropriate breaker, checks that power is off, and starts removing the old receptacle. Now the espresso machine is turned on. You will now have a current path from the other breaker, through the machine, back through the other wire to the outlet being repaired, and through the maintenance worker. Not generally considered good.

Now suppose the two receptacles are from different distribution transformers. When the espresso machine is turned on, there will be a complete path for current to flow from one breaker (on one panel) through the machine and to the other breaker (on the other panel). But that complete path must necessarily include the grounding electrode conductors of each of the two transformers, and the grounding electrode system. I would call that "objectionable current." And by the way, the hazard I describe above still exists for this situation as well.

If I were to come across this situation, I would be inclined to look for a way to get it shut down. Yes, I would deny espresso operators a chance to pursue their livelihoods, if by their doing so they pose a threat to someone else's life.

And as to the bit about ?It?s never been a problem before,? I will offer (once again) the following analogy,
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[ November 15, 2005, 11:16 AM: Message edited by: charlie b ]

 

[petersonra]

Re: 240v to Espresso cart using two 120 V out;lets

After reflection, and reading your post, I am inclined to agree with your analysis on the code and safety issues.

In any case, this practice is not what caused the melted wires.

 

[charlie b]

Re: 240v to Espresso cart using two 120 V out;lets

Originally posted by petersonra:In any case, this practice is not what caused the melted wires.

I agree. I also wonder if the ten food warmers could have done it.

The idea of protecting the branch circuit conductors is that if you plug in too many things, the breaker will trip before the wires can be damaged. So I would suggest looking into the protection scheme. Perhaps there is a bad breaker, or perhaps there is a 25 amp breaker and #14 conductors. Something is not right here.

 

[rcwilson]

Re: 240v to Espresso cart using two 120 V out;lets

Thanks for the comments. My original concern involved the current return path, induced currents and NEC Section 300.20.

With this two receptacle setup, the black wire in each EMT conduit to the receptacles is carrying current but there is no corresponding flow of current in the opposite direction in the neutral or any other wire in the conduit. The current is returning to a different panel through a different conduit.

I theorized that the induced circulating currents in the EMT may have increased the temperature at the already heavily loaded outlets. But how hot could an EMT conduit or fitting get with just 10A? The melted wires were probably from loose connections and overloads.

To solve the problem at church, we added 208V outlets plus several circuits just for the food warmers at the carnival.
.

 

[charlie b]

Re: 240v to Espresso cart using two 120 V out;lets

Originally posted by rcwilson:I theorized that the induced circulating currents in the EMT may have increased the temperature at the already heavily loaded outlets. But how hot could an EMT conduit or fitting get with just 10A?

I hadn't thought of that. Perhaps it might have been a contributing cause after all. I don't recall how to do the math anymore (magnetic fields were never really friends of mine). But I would not call it impossible that even 10 amps could create a strong enough field to cause overheating.