800A disconnect with parallel 400A fuses - pic

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bbaumer

Senior Member
Location
Indiana
Don't really have a question, just never seen one of these until today. Thought I would share.

800A, 120/240V single phase. Parallel fuses clips with 400A fuses.
 

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bbaumer

Senior Member
Location
Indiana
Oh, the line side has parallel 500's plus a "tap-ahead-of-the-main" over to an emergency panel. Load side is parallel 500's. This is the service disconnect for the building.

It also looks like this switch could accommodate another set of fuse holders as well and be converted to 3 phase.

Thought it was interesting.
 
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GoldDigger

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Location
Placerville, CA, USA
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Don't really have a question, just never seen one of these until today. Thought I would share.

800A, 120/240V single phase. Parallel fuses clips with 400A fuses.

Have never seen one either. Paralleling fuses in listed equipment designed for that use (as this certainly appears to be) is allowed. But there should be a caution that to avoid nuisance trips it is important that the paralleled fuses should be the identical type from the same manufacturer, and if possible of the same age, etc.
If for some reason (other than a trip, which will blow both!) you need to replace one, you should replace both.
 

brian john

Senior Member
Location
Leesburg, VA
This was the norm for large services and FSS (fused safety switches) in pre-800 and larger fuses. Can't tell you when this type of installation ended.
 

Jraef

Moderator, OTD
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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
This was the norm for large services and FSS (fused safety switches) in pre-800 and larger fuses. Can't tell you when this type of installation ended.
I've also seen it done when vertical space was limited. 400A fuses are a lot shorter than 800A fuses. An 800A Fused switch would take up an entire bay height, a 400A switch would not.
 

bbaumer

Senior Member
Location
Indiana
It looks to me that each phase is in it's own conduit?

Yep. A guy I work with noticed that right off too.

The service entrance conductors are A-B-N in each pipe into a CT cabinet just to the left of this switch. The installer nippled between the CT cabinet and the disconnect and grouped them A-A-N and B-B-N through the nipples.

My co-worker, pardon me for this, felt the nipples to see if they were warm. From magnetic inductance of course. They were not.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
Yep. A guy I work with noticed that right off too.

The service entrance conductors are A-B-N in each pipe into a CT cabinet just to the left of this switch. The installer nippled between the CT cabinet and the disconnect and grouped them A-A-N and B-B-N through the nipples.

My co-worker, pardon me for this, felt the nipples to see if they were warm. From magnetic inductance of course. They were not.

That made me laugh.:lol:

Curiosity would have gotten the better of me too, I would of felt them also.:ashamed1: They must not have much current going through them.
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The installer nippled between the CT cabinet and the disconnect and grouped them A-A-N and B-B-N through the nipples.
Leaving the nipple piercing analogies aside for the moment, is it code to have the two parallel neutrals running through different nipples? (If they are in fact parallel.)
 

kwired

Electron manager
Location
NE Nebraska
Leaving the nipple piercing analogies aside for the moment, is it code to have the two parallel neutrals running through different nipples? (If they are in fact parallel.)

If they are in parallel then there should be one in each pipe. There should also be a line 1 and a line 2 in each pipe, instead this install has L1,L1, N in one pipe and L2,L2,N in the other pipe.
 
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