corrosion and voltage on neutral

B

bitcoin miner

Member
Location
Marble , NC
Occupation
facilities maintenance
As my user name suggests, I work for a company that mines bitcoin. It's a very power hungry application. My site uses about 100megawatts of power from two differnt power company feeds, one from TVA and one from Duke Energy. On the Duke energy side we see low voltage on the neutrals, not enough to hurt you but plenty enough to make you question LOTO. In one particular building we have 90 breaker panels with 42 20 amp breakers installed that go to 42 240volt outlets built into the side of the panels. We have miners plugged into the outlets. These panels are bottom fed through a 3" pvc conduit with 4ought aluminum wire. Everything is torqued properly with anti-ox compound. Some of the panels are getting moisture inside which gets in the outlets causing the plugs to blow out of the outlets. The 20 amp breaker for the outlet never trips but now and then the 225 amp main breaker feeding the panel will trip. It usually resets and we watch for a few minutes to see which outlet lets the smoke out and we unplug that particular machine. We have replaced a number of these panels and have started putting expanding foam in the conduit to try and eliminate any moisture from getting in the panel. That has only worked slightly.
My question to the group are:
What can cause the moisture intrusion?
Does the low voltage on the neutral contribute to the corrosion?
Why aren't the outlet breakers tripping when the moisture causes a dead short?
 
Sealing your ug conduits is a good start. The typical expanding foam from a big box is not listed for use in sealing conduits
Polywater makes a suitable product that I have used and works well.
Duct seal is a the most common product, it just takes time to push it around all the wires, I warm it up first
 
To start how do you think that moisture is entering the panels? Obviously this is not a normal condition.
 
Do you have the panels in an unconditioned environment with conduits leading into a cooled equipment room?
are you controlling the humidity in your environment?
 
bitcoin miner said:
The 20 amp breaker for the outlet never trips
Click to expand...
The Main operates faster than branch breakers.

To isolate faults at branch outlet before it smokes, 20 amp GFCI breakers should trip before the Main, since water is not the best conductor.

The typical practice for wet locations is to tape receptacle terminals, and the requirement is to make sure raceways and outlet boxes are arranged to drain.
 
Presumably by low voltage on the neutral you mean a few volts n-g. This is pretty common and caused by the voltage drop in the neutrals going back to the n-g point.

As for water getting in your conduits you cannot prevent it so sealing them is not the solution. Figure out a low point in every piece of conduit and install a drain there, drill a weep hole.
 
If I could figure out how to post pictures I would show you what this particular installation looks like.
The biggest hurdle to face mining is getting rid of the heat produced. Picture 16' tall racks 200' long with a thousand miners on those racks. There are two of those racks that face each other with about 20' separating them. That middle section is open to the atmosphere with a roof about 60' up. These racks are inside a fabric building with filter walls to allow air in to help cool the miners. Our transformers are outside and switchgear are inside. The original plan was to go with wire trays from the switchgear to the racks but whoever designed the building didn't have enough structure to support the wire trays. No problem, they cut the concrete and installed underground conduits. When I looked through the conduits with my borescope I can see some of the pipes have collapsed and they have water in them. That's why we initially thought the moisture was coming from the conduits but still not sure. The panels are technically inside but with the filter walls they are still exposed to humidity and temperature changes. The panels are on the cool side but we are considering creating openings from the hot side to the cool side where the panels are to keep the temperature more stable. That would be fine right now but when the weather starts to warm that's not a solution.
I replaced a couple of the panels4 months ago and the ones I sealed with the spray foam have less corrosion but what's there will only get worse. One of the ones I replaced in June I just had to replace again. The moisture only appears to be affecting maybe 15 of the 90. My guess is I'll have to break up the concrete and replace the crushed pipes and/or any that have water in them. My thinking is that the water in the pipes gets heated to create steam and that's what is getting into my outlets causing them to short. That same steam may be ruining the breakers making them not trip. More than a third of the breakers don't have good continuity when I replace a panel.
Once I figure how to post pictures all this will make more sense.
 
ramsy said:
The Main operates faster than branch breakers.

To isolate faults at branch outlet before it smokes, 20 amp GFCI breakers should trip before the Main, since water is not the best conductor.

The typical practice for wet locations is to tape receptacle terminals, and the requirement is to make sure raceways and outlet boxes are arranged to drain.
Click to expand...
I have taped outlets in a couple of the panels and sprayed a couple with anti-corrosion spray. I am still getting liquid water coming out of them. I have been out working on one panel only to have outlets in the nearest panel literally blow the plugs out of the receptacles as the water creates a short and it steams up creating the loud pop. Very disconcerting. I'll see if I can find GFCI in that breaker style. Thanks
 
petersonra said:
Presumably by low voltage on the neutral you mean a few volts n-g. This is pretty common and caused by the voltage drop in the neutrals going back to the n-g point.

As for water getting in your conduits you cannot prevent it so sealing them is not the solution. Figure out a low point in every piece of conduit and install a drain there, drill a weep hole.
Click to expand...
That sounds like something that should've been done originally. When and if I have to break the concrete up I'll make sure they all have drain holes.
Does the low voltage n-g contribute to the corrosion?
Thanks
 
infinity said:
To start how do you think that moisture is entering the panels? Obviously this is not a normal condition.
Click to expand...
The panels are typical indoor panels with just a bolt on cover. The switchgear have cooling fans sucking the hot inside air out. This probably also creates a negative pressure in the panels which would pull in humid outside air condensing it on the cool metal surfaces. That's one theory. Water in the conduits is steaming off and rising up through the pipe into the panel. Theory number 2. I have placed desiccant packs with the panels near the conduit and on top the highest breaker. Those packs have the pink/blue indicators showing the presence of moisture. The panels I have sealed with the spray foam show no moisture on the packs but I'm still getting corrosion on the neutral bar. The panels I haven't used the spray foam in show moisture on the packs and more corrosion than the same age panels with the foam. My guess is the bulk of the moisture is coming from the conduit but not all of it. I was going to try a couple panel heaters to keep the air inside higher than the dew point but that's only a solution until it warms up. Any extra heat in the summer is no good and even with the higher ambient heat I still have a moisture problem. I have a similar building close by and it doesn't have this issue but it has all the wires from the switchgear overhead in cable trays connected to PDUs. That particular building has twice the number of miners and larger filter walls too.
I hate to think it but I believe I am fighting poor engineering. The building design was wrong and the fix wasn't the best plan. It's my job to keep them mining and making money but I want a permanent solution and not keep band aiding it.
 
jim dungar said:
Do you have the panels in an unconditioned environment with conduits leading into a cooled equipment room?
Click to expand...

Good question. Or perhaps it could be the reverse with the panels in a cooled equipment room, and there's a pressure differential that's bringing in more humid air into the panels from outside of the room. And then the more humid air condenses inside the panels, etc. As well as sealing conduits, perhaps the HVAC system could be reviewed to see if such a pressure differential exists, and if so could it be reduced. It might be difficult to completely seal off air intrusion coming through gaps between conductors in the conduits if a pressure differential exists.
 
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While I was composing my post #12 above, the OP made his post #11 mentioning pressure differentials causing air movement that could be bringing in humidity. I think that is a likely factor that's causing unwanted condensation.
 
bitcoin miner said:
I have taped outlets in a couple of the panels and sprayed a couple with anti-corrosion spray. I am still getting liquid water coming out of them. I have been out working on one panel only to have outlets in the nearest panel literally blow the plugs out of the receptacles as the water creates a short and it steams up creating the loud pop. Very disconcerting. I'll see if I can find GFCI in that breaker style. Thanks
Click to expand...
You said the voltage was 277. GFCIs are only for use on circuits where the voltage to ground does not exceed 150 volts.
 
bitcoin miner said:
The panels are typical indoor panels with just a bolt on cover. The switchgear have cooling fans sucking the hot inside air out. This probably also creates a negative pressure in the panels which would pull in humid outside air condensing it on the cool metal surfaces. That's one theory.
Click to expand...

Could you have some fans/ blowers that take in conditioned lower humidity air and feed it into the problem areas to reduce the amount of negative pressure pulling in humid air?
 
bitcoin miner said:
That sounds like something that should've been done originally. When and if I have to break the concrete up I'll make sure they all have drain holes.
Does the low voltage n-g contribute to the corrosion?
Thanks
Click to expand...
The low voltage won't cause corrosion.

You can drill weep holes in conduit fittings without disassembling anything.
 
bitcoin miner said:
blow the plugs out of the receptacles as the water creates a short and it steams up creating the loud pop.
Click to expand...
Arrange raceways to drain, before equipment floods.

Flooded underground raceways should have a stub up into the panels.

After power shutdown, can plumber route water to outside drains by tapping those stub ups?

If equipment remains in wet location, from exterior intrusions, you need wet location listed equipment.
bitcoin miner said:
I'll see if I can find GFCI in that breaker style. Thanks
Click to expand...
If still needed after drain, 240v GFCI breaker disconnects are mass produced by each manufacturer.
 
ramsy said:
.....240v GFCI breaker disconnects are mass produced by each manufacturer.
Click to expand...
I know of no 240V Line to Neutral GFCI manufactured by any major breaker manufacturer.
I do know of many GFPE or GFP breakers, but relatively few that are intended for what appear to be single pole 240V breakers in the OP.
 
jim dungar said:
I know of no 240V Line to Neutral GFCI manufactured by any major breaker manufacturer.
I do know of many GFPE or GFP breakers, but relatively few that are intended for what appear to be single pole 240V breakers in the OP.
Click to expand...
You've never seen a hot tub disconnect?

Op in #1 said 240v outlet. Don't see 240v to ground?
 
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