improperly grouped service entrance conductors in old service

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sunny1

sunny1

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Location
Washington State
Occupation
electrician
Hello,

I have recently discovered two old 4 wire three phase 208/120 services where the conductors are improperly divided into two rigid steel conduits. One is a four hundred amp service fed by two parallel runs of 250 kcml AL. For some reason they ran all of the conductors in one piece of ridgid except for one grounded conductor, which is alone in a seperate piece of rigid. I'm guessing because they couldn't quite jam all of the wires through the one pipe (?)

the second service feeds a 200 amp panel and has two longer runs of 2" rigid, one has two hots and the other has a hot and the neutral. In both cases the rigid enters steel enclosures.

There is a laundry list of violations on both services that were easily identified, but I am specifically concerned with 300.3(b) as I don't have a clear grasp of the hazards of inductive heating or any other potential problems. These installations are at least 40-50 years old, but I am concerned adding loads could suddenly awaken a sleeping dragon. Any explanations of what we are up against would be greatly appreciated!
 
Welcome to the forum.

You're absolutely correct about these issues.

What is your actual question?
 
Sorry for the long winded explanation without a specific question! I guess I was just hoping to get opinions/ hear stories of other folks’ experience with this kind of problem.

Is it as simple as increasing the load increases the danger or is it more a matter of how the load is balanced, or what kind of loads are being served? I must admit i don’t have the knowledge of theory to grasp the scope of the hazard

unfortunately in both cases the conductors are direct buried between the building and the transformer so fixing the problem will be no small feat. I am fully prepared to try to sell new services to my boss, our facilities manager, but his first question will be ‘so why is this 40 year old service suddenly dangerous?’ and I don’t have a great answer yet. Any insight would be much appreciated!
 
We had a customer that had at one time been a 480 ungrounded, or maybe a corner ground. No one remembered. Eventually the POCO changed them to a Wye. The solution was to add the fourth wire in separate conduit. No noticeable issue. No neutral load.

Another location had two neutrals to the building tapped at different points of the poletop type transformer bank. They also entered the building and were bonded at different points. We always had 40 amps of current flow on the neutrals with No neutral load. We removed the ‘one’ that made no sense and no more Amp on neutral.
 
sunny1 said:
Sorry for the long winded explanation without a specific question! I guess I was just hoping to get opinions/ hear stories of other folks’ experience with this kind of problem.

Is it as simple as increasing the load increases the danger or is it more a matter of how the load is balanced, or what kind of loads are being served? I must admit i don’t have the knowledge of theory to grasp the scope of the hazard

unfortunately in both cases the conductors are direct buried between the building and the transformer so fixing the problem will be no small feat. I am fully prepared to try to sell new services to my boss, our facilities manager, but his first question will be ‘so why is this 40 year old service suddenly dangerous?’ and I don’t have a great answer yet. Any insight would be much appreciated!
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Grappled with that question many times. Most that ask this have the mentality "if it ain't broke, don't fix it" (iiab,dfi) and see electricity as the lights come on and anything else is "it ain't broke". They say it's been that way for 40yrs, it must not be that bad, so why does it suddenly need to be "fixed"? I'd like to know a good answer other than the code says it must be this way not that, or safety, that might convince the category of persons iiab,dfi.
 
The few times I've been down that road, I start with the word "suddenly"; it doesn't "suddenly" need to be fixed, it's needed that for years but nobody did, every day is another failure dice roll. Or, I haven't been a car crash for a while, but wear my seat belt anyway.

Sometimes, the appeal to preventative maintenance works "You do PM on the machines, right? This needs it, too."
 
The issue of inductive heating is essentially that of the metal conduit acting as the secondary of a transformer. Current flows in your circuit wires, and this induces current to flow in your conduit.

How much this is a problem depends upon the net current flowing in the 'primary' of this unintended transformer and the impedance/resistance of the 'secondary'. The magnetic properties of the conduit are also a factor.

You say that the conductors are 'direct buried', which implies that the conduit system is not continuous. If this is the case then it is possible that you don't have a conduit 'circuit' which would greatly reduce any sort of inductive heating issues. Of course if you have lengths of conduit at the start and end of a direct buried run, then you will still see some conductivity between the conduit ends (conduction through the soil), and you might also have direct metallic connection underground creating the undesired loop.

The balance of loads on the conductors are also a factor. In your example of 2 phases in the first conduit and phase/neutral in the second, imagine that the panel is loaded so that you only have L-L loads between the first 2 phases, and only L-N loads on the third. There would be no net current on the separate conduit runs, and no induced heating. (Note this is a very unlikely loading, just an example showing that the particular loading/balance matters.)

A separate factor from inductive heating is that you can have a 'choke' effect which will reduce fault current and may cause circuit breakers or fuses to take longer to clear a fault.

-Jon
 
Unless you can show that something is an actual hazard, it is going to be hard to get someone to lay out a bunch of money to "fix" something that has been working for decades.

I guess a lot depends on what your role in the mess is.

My personal opinion on electrical systems of this age is that it is not worth trying to fix them. They are at an age when it is probably better to replace, and realistically, that may be what you have to do if you end up getting paid to bring them up to code.
 
winnie said:
The issue of inductive heating is essentially that of the metal conduit acting as the secondary of a transformer. Current flows in your circuit wires, and this induces current to flow in your conduit.

How much this is a problem depends upon the net current flowing in the 'primary' of this unintended transformer and the impedance/resistance of the 'secondary'. The magnetic properties of the conduit are also a factor.

You say that the conductors are 'direct buried', which implies that the conduit system is not continuous. If this is the case then it is possible that you don't have a conduit 'circuit' which would greatly reduce any sort of inductive heating issues. Of course if you have lengths of conduit at the start and end of a direct buried run, then you will still see some conductivity between the conduit ends (conduction through the soil), and you might also have direct metallic connection underground creating the undesired loop.

The balance of loads on the conductors are also a factor. In your example of 2 phases in the first conduit and phase/neutral in the second, imagine that the panel is loaded so that you only have L-L loads between the first 2 phases, and only L-N loads on the third. There would be no net current on the separate conduit runs, and no induced heating. (Note this is a very unlikely loading, just an example showing that the particular loading/balance matters.)

A separate factor from inductive heating is that you can have a 'choke' effect which will reduce fault current and may cause circuit breakers or fuses to take longer to clear a fault.

-Jon
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Thanks a lot Jon! Hugely helpful post. your example of thinking of the conduits as secondarys on a transformer especially helped me understand and visualize the problem.
 
petersonra said:
Unless you can show that something is an actual hazard, it is going to be hard to get someone to lay out a bunch of money to "fix" something that has been working for decades.

I guess a lot depends on what your role in the mess is.

My personal opinion on electrical systems of this age is that it is not worth trying to fix them. They are at an age when it is probably better to replace, and realistically, that may be what you have to do if you end up getting paid to bring them up to code.
Click to expand...
I agree I would really like to see them both completely redone. My role in this mess is has so far been to add new circuits to the system which had never involved taking the cover off of the Main disconnect where the problem exists. But now that i’ve seen it, and thanks to posts on this thread, have a better understanding of it, I can’t unsee it.
 
zbang said:
The few times I've been down that road, I start with the word "suddenly"; it doesn't "suddenly" need to be fixed, it's needed that for years but nobody did, every day is another failure dice roll. Or, I haven't been a car crash for a while, but wear my seat belt anyway.

Sometimes, the appeal to preventative maintenance works "You do PM on the machines, right? This needs it, too."
Click to expand...
Right because the ‘suddenly’ will be when the electrician (me most likely, or the next guy) adds the wrong load to the system. I’m pushing for new services
 
We’ve had to fix this in industrial plants. Cut the enclosure out where the wiring enters/exits. Put aluminum in where the cutout hole is at. Nonferrous does not cause the inductive heating issues.
 
paulengr said:
We’ve had to fix this in industrial plants. Cut the enclosure out where the wiring enters/exits. Put aluminum in where the cutout hole is at. Nonferrous does not cause the inductive heating issues.
Click to expand...
Ah hah. That's a solution I hadn't thought of. It's looking like we are putting a project together to seek funding to replace the whole service. the closer we looked, the more issues we found all the way back to how they made up the CT can that feeds both buildings. Thanks for the input!
 
Anything over 30 yrs old unless immaculate gets this scrutiny. Furthermore with mains this old how would you safely know if the mechanical aspects of the breaker works. Something that sits for 30 or 40 years that has never been turned off and on may not shut off or reset. Replace this old stuff
 
Most times when we shut off an old enclosed main especially mobile home ones that are not 2' off the ground with weeds and trees grown in all around them we warn the customer they may be on the hook for a new main if it won't flip back on before we shut it off
 
Poweranytime said:
Most times when we shut off an old enclosed main especially mobile home ones that are not 2' off the ground with weeds and trees grown in all around them we warn the customer they may be on the hook for a new main if it won't flip back on before we shut it off
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Ya I am always afraid to switch off old mains have you ever had one not turn back on?
 
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