Feeder tap question

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CaliforniaMike

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All,
I used to be an EE, many years ago, so I just got pulled into a review of an old (>70 year) oven on our production floor. I have not looked at the NEC since about 2005 so I am more than rusty. I would appreciate it if I could get a quick reality check.

The oven is supplied with 3 phase 240 by a 150 amp breaker about 25 feet away and power is landed on an abandoned 3 phase contactor with what looks to be 50 year old 2/0. From here, there are many (>10) small gauge (18-12 AWG) wires all smashed together to land on another terminal on each of the poles of the contactor terminals on the same side of the contactor as the landing. (The switched side is abandoned.) These wires then run through the oven, under the heated zone, to another panel with breakers. The entire length of these wires is enclosed in the oven, but not protected in any other way. All of the cloth insulation is fraying. The interpretation seems to be that these wires are taps.

We have an oven in house, but it may take a week or more to get ready to replace the older oven.

I have visions of 36 kW finding a way home through 18 AWG conductors so my instinct was to simply shut down the older oven until the new oven is ready to power up.

Barring this, my basic suggestions were that:

1) While we probably comply with the disconnect requirements, it would take someone that was not familiar with the oven several minutes to find it and we should just put one on the oven at the point of power entry. Short term, we should at least train everyone that works on the floor on the location of the disconnect.

2) If we wanted to run the existing oven, the wires from the 2/0 needed to directly land on some kind of distribution board and directly feed breakers, not run all over an oven on the way to some breakers.

Am I overreacting?

Thanks,

Mike
 
First of all, you are not overreacting. My assessment is that the proper immediate course of action would be to have an electrician disconnect the wires at the 150 amp breaker feeding this monster, and then wrap chains with heavy padlocks around the beast until it can be tossed into the nearest ocean. But I have a few questions.

Is this thing presently in service? What does (or did) it do (i.e., what gets heated by this oven - food or products being manufactured)? In what sense does this thing have breakers (i.e., what do the breakers feed)?
 
I would not get excited about it just yet. Is this a factory configuration? Sounds like all somebody did was move the wires from one side of the contactor to the other which doesn't really change anything. I would consider these smaller gauge wires as taps. Problem is that the national electrical code does not recognize individual wires as small as number 18. So unless this is part of a factory assembly I think you have a problem there as well. On the other hand if it's been running for God knows how many years I would not be turning the plant off without a closer look at what is actually going on.

I don't know what you mean by smashed together either. There are certainly ways that you could legally connect the smaller wires to the large wire at the contactor. Wether that was done or not is not clear
 
These so called "tap wires" part of the appliance?

Is it listed appliance, if so are they original condition other than possibly they are now bypassing the mentioned contactor?
 
Thank you for the prompt responses. Sorry to drop off the edge of the world. My account got disabled and it took a while to sort out.

charlie b said:
First of all, you are not overreacting. My assessment is that the proper immediate course of action would be to have an electrician disconnect the wires at the 150 amp breaker feeding this monster, and then wrap chains with heavy padlocks around the beast until it can be tossed into the nearest ocean. But I have a few questions.
This was the polite version of my initial reaction.

Is this thing presently in service?
It was cleaned up, some. I believe that it is now scheduled to be retired in the near future.

What does (or did) it do (i.e., what gets heated by this oven - food or products being manufactured)?
The oven is used to heat parts prior to a plastic molding operation in a production plant.

In what sense does this thing have breakers (i.e., what do the breakers feed)?
There is a dedicated 250 Amp breaker on a wall, but it is about 50 feet away, on a wall with about half a dozen other dedicated panels. Technically in site of the operator. However, anyone else in the plant would probably take quite a while to find this breaker.

This breaker directly feeds the oven where it is landed inside the over on an abandoned three phase contactor with doubled input lugs. Power lands on one of these for each phase, and is then fed to a collection of smaller breakers on the other size of the machine. These breakers then feed about a dozen heating zones. The wires from the power "landing" to these smaller breakers are simply pulled through the machine, around the heating zones, and are in no sense rated for 250 Amps.
Click to expand...
 
LarryFine said:
It sounds like the contactor was bypassed.
Click to expand...
Agreed. However, it looks like they also abandoned the original landing and over overcurrent protection and put in a series of breakers on the other side of the machine to protect the lower power heating zones. To bridge this, they simply pulled small gauge wires from the 250 Amp line and ran them through the machine. My thought is that these are not taps, and if one of them shorted...
 
petersonra said:
I would not get excited about it just yet. Is this a factory configuration? Sounds like all somebody did was move the wires from one side of the contactor to the other which doesn't really change anything. I would consider these smaller gauge wires as taps. Problem is that the national electrical code does not recognize individual wires as small as number 18. So unless this is part of a factory assembly I think you have a problem there as well. On the other hand if it's been running for God knows how many years I would not be turning the plant off without a closer look at what is actually going on.

This is sort of where we ended up, very temporarily. Part of the issue is that, well, in my opinion, this just is not right. Second, we now have knowledge that it is there. Last, as part of the repairs that prompted this finding, all this old stuff, including crumbling insulation, have been disturbed. One of my fears is that with all this small stuff tapping off a 250 Amp feeder and then running unprotected all over the machine, we might get into an arc flash issue. This has been raised and is being considered in the plans to, I believe, phase out this oven in the near term.

I don't know what you mean by smashed together either. There are certainly ways that you could legally connect the smaller wires to the large wire at the contactor. Wether that was done or not is not clear
Click to expand...

The contactor has a large double lug on each phase of what would have been the input side of the contractor. The power is landed on one of the double lugs. Many small wires of several gauges were then stripped and twisted together and then "landed" in the other side of this lug (not contactor) and held in place with the single screw for this side of the terminal.
 
kwired said:
These so called "tap wires" part of the appliance?

Is it listed appliance, if so are they original condition other than possibly they are now bypassing the mentioned contactor?
Click to expand...
I can not be certain. However, it does not seem like this is original wiring. My experience was with larger stuff, but we would never have considered something a tap unless it was contained and went directly to a very local method of OC protection. Again, this is a bit out of my comfort zone.
 
I repeat my assessment.

I have seen plenty of appliances with several small wires fed from a single larger input terminal; not our concern.
 
LarryFine said:
I repeat my assessment.

I have seen plenty of appliances with several small wires fed from a single larger input terminal; not our concern.
Click to expand...
yes that does happen, but those appliances are typically listed that way. If this has been modified over it's lifetime there may be valid concerns.
 
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