400A service?

[FionaZuppa]

I am a pretty practical guy and it seems very unlikely that any manufacturer produced a 400 amp rated fused switch that could accept 800 amps of overcurrent protection. I won't say it is not possible, just unlikely.


It should go without saying that if this switch is actually labeled as 400 amp that it should not be used beyond that.

its only 800A because someone put in two 400A fuses. someone could have put in 800A fuses.
the other disco he mentions, says that is a 400A disco, but if its using std size fuse anyone can stick a 800A fuse in there.

 

[iwire]

its only 800A because someone put in two 400A fuses. someone could have put in 800A fuses.

No.



200 amp fuses are one frame size

400 amp fuse are another frame size

800 amp fuses are another frame size.

If you where making a 400 amp switch with parallel fusing the fuse holders would only accept up to 200 amp fuses.

It seems you do not understand the physical dimensions of fuse are diffrerent.

 

[kwired]

if the other disco has about same physical dimensions on contacts and uses what looks like same materials, and its marked "400A", then i might say the one with two fuses has same rating. not 100% but a good hypothesis. ??

Don't forget this unit is likely old enough they didn't pay much attention to having necessary conductor space like they do today, I've seen newer 400 amp switches that are bigger then some older 800 amp switches that are out there, not because the fuses are any different - they actually have room to bend conductors in the newer equipment.

 

[FionaZuppa]

No.



200 amp fuses are one frame size

400 amp fuse are another frame size

800 amp fuses are another frame size.

If you where making a 400 amp switch with parallel fusing the fuse holders would only accept up to 200 amp fuses.

It seems you do not understand the physical dimensions of fuse are diffrerent.

so, whatever the biggest fuse fits the holder is what determines the disco rating? in this case two 400A fuses fit so its at least a 800A disco? from the pics i doesnt look like any longer fuse would fit. i thought when i looked up this fuse type they listed other amp ratings but were same size, but i could have been wrong.

 

[iwire]

so, whatever the biggest fuse fits the holder is what determines the disco rating?

Not really, the labeling of the disconnect determines the rating.

But if you are producing a disconnect switch rated / labled 400 amps with parallel fuses it seems highly unlikely you would put in a pair of 400 amp fuse holders, you would put in a pair of 200 amp fuse holders that could directly handle 110 through 200 amp fuses and with fuse reducers could handle any size fuse less than 200 amps.

We are spending a lot of time on this, it would be nice if the OP could give us the label info off of this disconnect.

in this case two 400A fuses fit so its at least a 800A disco?

That is what I believe, it would be nice to verify it.

from the pics i doesn't look like any longer fuse would fit.

Once we go to fuses larger than 602 amps they become bolt in, not 'push in' so if they had wanted to make an 800 amp disconnect with single fuses they design would be much different.

I should mention I have not seen every fuse and there are many types but in my experience above 602 amps fuses must be nut and bolted into place.

 

[FionaZuppa]

Not really, the labeling of the disconnect determines the rating.

But if you are producing a disconnect switch rated / labled 400 amps with parallel fuses it seems highly unlikely you would put in a pair of 400 amp fuse holders, you would put in a pair of 200 amp fuse holders that could directly handle 110 through 200 amp fuses and with fuse reducers could handle any size fuse less than 200 amps.

We are spending a lot of time on this, it would be nice if the OP could give us the label info off of this disconnect.




That is what I believe, it would be nice to verify it.



Once we go to fuses larger than 602 amps they become bolt in, not 'push in' so if they had wanted to make an 800 amp disconnect with single fuses they design would be much different.

I should mention I have not seen every fuse and there are many types but in my experience above 602 amps fuses must be nut and bolted into place.

i think OP mentioned that the dual fuse disco had no markings, probably a paper label that fell off 20yrs ago. but OP did mention the two discos were similar but the one had dual fuses. back in those days i suspect it was easier to just build the same unit with perhaps a variation of fusing to make products that were of different ratings, even if that meant that the lower rated disco used the exact same materials which would be technically over-engineered. now days manufacturers use minimum amounts of materials that will meet the specifications.

 

[PetrosA]

Update 7/11

I went back today to see what I could find that I didn't look for the first time I was there (Remember, I wasn't there to check the gear, only to seal the conduits entering the building).

There IS an inspection sticker on the house panel. I can't read it anymore, so I don't know if it's a final or service or what. Different agency than what's in the other building, so these two buildings must have been built at different times or had totally different contractors build them.

The switch was made by Clark American from Cincinnati. There is a paper with a schematic and rating, but I can't make out what the rating is. It looks like a three digit number ending in two zeros, but that covers a lot

I tried to get decent pictures, but my phone camera is worthless. If anyone recognizes the equipments, let me know.

 

[PetrosA]

Here's a shot of the disconnects in the other building for comparison. There's also an aerial shot of both buildings.

 

[augie47]

If I recall correctly, that was the trademark of Joslyn Clark Controller Co.
The first company I worked for had a number of their switches and the building dated back to 1928. I recall seeing some of the double fuse switches but no details.
A 1947 NEC Handbook notes that fusible switches above 600 anps employed double fuses (apparently larger fuses were not manufactured)

 

[kwired]

Update 7/11

I went back today to see what I could find that I didn't look for the first time I was there (Remember, I wasn't there to check the gear, only to seal the conduits entering the building).

There IS an inspection sticker on the house panel. I can't read it anymore, so I don't know if it's a final or service or what. Different agency than what's in the other building, so these two buildings must have been built at different times or had totally different contractors build them.

The switch was made by Clark American from Cincinnati. There is a paper with a schematic and rating, but I can't make out what the rating is. It looks like a three digit number ending in two zeros, but that covers a lot

I tried to get decent pictures, but my phone camera is worthless. If anyone recognizes the equipments, let me know.

I recognize the Square D breaker/enclosure on the far left in the first picture

Sorry not much help on the rest of the equipment. I would guess that paralleled fuses like that must have been acceptable at one time or they likely wouldn't have made such a unit.