Grounding a XFRMR

[mstrlucky74]

When grounding a transformer if you had the scenario as shown in the attachment then obviously your not grounding to building steel/electrode(250.30(A)(4). Don't see why you would install what's designed in the attachment unless there wasn't building steel.
It's one or the other correct? Thanks.

 

[infinity]

If there is building steel then that ground bus would be connected it to it somehow. Not sure why they're showing a 400 kcmil Al conductor when the largest ever required would be 250 Al.

 

[mstrlucky74]

If there is building steel then that ground bus would be connected it to it somehow. Not sure why they're showing a 400 kcmil Al conductor when the largest ever required would be 250 Al.

Yes but wouldn't the other option be to connect each xfrmr locally to bldg. steel?

 

[infinity]

Yes but wouldn't the other option be to connect each xfrmr locally to bldg. steel?

If it had building steel then that's normally what you would use. Common grounding electrodes are typically for poured concrete buildings.

 

[publicgood]

It is all about accessible/inspectable ground points in each electrical room. It is also a place to group other bonded elements in the room such as raised floor and cable tray.

For all designs, both post tension construction and steel buildings, we typically design with a ground bar in every electrical room and tie them together with 3/0. Yes, in a VE exercise we could simply call for the ground bar to be bonded to steel within each room. Although, short of agreeing on mechanical connections, each welded connection to steel may effect the galvanization of the steel, which we prefer to keep to a minimum.

For telecommunications BICSI has us with a ground bar in each telecommunication space and tied back to the entrance room - size depending on which version of TIA.

 

[mstrlucky74]

Thank you

 

[mstrlucky74]

Just to be clear if the building has rebar within columns/decks that building steel, correct?

 

[GoldDigger]

Just to be clear if the building has rebar within columns/decks that building steel, correct?

No, since the interconnection of the various sets of rebar cannot be counted on.
Building steel refers to a steel girder construction which supports concrete or other wall, floor and roof materials.
You know the girders are attached firmly to one another.

 

[mstrlucky74]

No, since the interconnection of the various sets of rebar cannot be counted on.
Building steel refers to a steel girder construction which supports concrete or other wall, floor and roof materials.
You know the girders are attached firmly to one another.

Lol.. got it. I'll check structural dwgs.

 

[mstrlucky74]

No, since the interconnection of the various sets of rebar cannot be counted on.
Building steel refers to a steel girder construction which supports concrete or other wall, floor and roof materials.
You know the girders are attached firmly to one another.

When xfrmrs get grounded to building steel don't they usually get tied to the rebar? I for some reason remember on one job concrete being chop away to gain access to the rebar and that's what the xfrmr was grounded to.

 

[infinity]

When xfrmrs get grounded to building steel don't they usually get tied to the rebar? I for some reason remember on one job concrete being chop away to gain access to the rebar and that's what the xfrmr was grounded to.

You cannot just chop out some concrete and connect the GEC to a piece of rebar.

 

[mstrlucky74]

You cannot just chop out some concrete and connect the GEC to a piece of rebar.

Ok, thanks.

 

[mstrlucky74]

Building Steel!!

 

[infinity]

Building Steel!!

That is not building steel which is an electrode according to the NEC. It's simply an isolated piece of steel supported by a poured concrete structure.

 

[mstrlucky74]

That is not building steel which is an electrode according to the NEC. It's simply an isolated piece of steel supported by a poured concrete structure.

Why is it not? Then what is and how would I identify such? I know another poster mentioned girders. :?:?

 

[infinity]

Should look like this with the steel columns originating at the footings.

 

[mstrlucky74]

Should look like this with the steel columns originating at the footings.

Got it.

 

[petersonra]

Got it.

take a look at the requirements found in 250.50(A)(2).

 

[mstrlucky74]

take a look at the requirements found in 250.50(A)(2).

Will do, thanks