Grounding for an 800 amp disconnect feeding a boiler

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robert8717

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Seattle Wa
Hello,

My question involves a ungrounded 800 amp disconnect that feeds a boiler. The building that this boiler is in is from the 1930s. I am an inside wireman electrician but usually I am given a drawing about what wire to pull and all the other details. Therefore I would appreciate it if someone could point me to the correct code sections.

I have not gone to visit the site yet. here are the facts I know thus far.
1) 800 amp disconnect does not have a grounding conductor (green wire / bare wire)
2) The conduit that feeds the boiler from the disconnect is run over head in an accessible ceiling
3) This boiler is not original building equipment but nobody can tell me how old it is
4) I believe this is a 480 volt three phase system but I do not know yet for sure


Here are my thoughts about this thus far.

1) I went to table 250.122 and read that this system would require 1/0 grounding conductor
2) Can the grounding( green wire) conductor be on the outside of the conduit?
3) If so, can it be a bare copper wire
4) I do not know if the circuit that feeds this disconnect has a grounding conductor or not
5) At what point is it when the conduit can not count as the equipment ground?



I will update this with more details when I got visit the site, any input would be appreciated

Thank you,
Robert
 
robert8717 said:
Hello,

My question involves a ungrounded 800 amp disconnect that feeds a boiler. The building that this boiler is in is from the 1930s. I am an inside wireman electrician but usually I am given a drawing about what wire to pull and all the other details. Therefore I would appreciate it if someone could point me to the correct code sections.

I have not gone to visit the site yet. here are the facts I know thus far.
1) 800 amp disconnect does not have a grounding conductor (green wire / bare wire)
generally not required.
2) The conduit that feeds the boiler from the disconnect is run over head in an accessible ceiling
does not matter where the conduit is run
3) This boiler is not original building equipment but nobody can tell me how old it is
also not relevant
4) I believe this is a 480 volt three phase system but I do not know yet for sure
voltage is not relevant either

Here are my thoughts about this thus far.

1) I went to table 250.122 and read that this system would require 1/0 grounding conductor
if you use a wire style EGC
2) Can the grounding( green wire) conductor be on the outside of the conduit?
no
3) If so, can it be a bare copper wire
a bare wire is a legal EGC but it has to be inside the conduit with the other circuit conductors to be a legal EGC
4) I do not know if the circuit that feeds this disconnect has a grounding conductor or not
may or may not matter
5) At what point is it when the conduit can not count as the equipment ground?
metal conduit can be the sole EGC the whole way short of a few special cases such as medical facilities and I think classified areas.

I will update this with more details when I got visit the site, any input would be appreciated

Thank you,
Robert
Click to expand...

I don't see an obvious problem here. Metal conduit is a perfectly acceptable EGC.
 
I do not think I can use the conduit as an egc

I do not think I can use the conduit as an egc

If I am reading the code correctly according to 250.118 (2) b. I can not use the conduit as a ground because it is over 20 amp circuit conductors.

Is is that right?

robert
 
robert8717 said:
If I am reading the code correctly according to 250.118 (2) b. I can not use the conduit as a ground because it is over 20 amp circuit conductors.

Is is that right?

robert
Click to expand...
No you are not reading it right. 250.118 (2), (3), (4) are most likely what applies.

The only way (5) would apply is if you are using flex or sealtite and that is where (a), (b), (c) and (d) are referenced to.
 
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