# 200 amp 3 phase fused pull out 150 amp fuses



## frank1023 (Mar 19, 2013)

i have a question on a service i have seen feeding a bank main lug panel.

the main is a fused 3 phase pullout rated for 200 amps. 1/0 thhn feeding it on the line side and 1/0 feeding it on the load side 70 feet away to the main lug panel. The fuses are 150 amp each. Is this acceptable? 

just curious because if a fuse blows whats stopping a handyman from replacing it with a 200 amp fuse, in that case the wire size is inadequate for the fuse.


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## papaotis (Jun 8, 2013)

IMO it is just fine. wire and fuses rated proberly, but should be marked very boldly '150a fuses only'


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## micromind (Aug 11, 2007)

This is one of two reasons why I will not install fuses as service equipment. Of course, just about anyone will install the largest possible fuse if one of them blows. 

The other reason is if one of them blows, every 3Ø motor is in serious peril. Even if properly protected.


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## Southeast Power (Jan 18, 2009)

frank1023 said:


> i have a question on a service i have seen feeding a bank main lug panel.
> 
> the main is a fused 3 phase pullout rated for 200 amps. 1/0 thhn feeding it on the line side and 1/0 feeding it on the load side 70 feet away to the main lug panel. The fuses are 150 amp each. Is this acceptable?
> 
> just curious because if a fuse blows whats stopping a handyman from replacing it with a 200 amp fuse, in that case the wire size is inadequate for the fuse.


Same thing that stops people from increasing the size of a circuit breaker.
Usually as a point of maintenance, especially for a main, the load isn't going to change and the branch circuit OCP is really doing the job of protecting the panel guts.
Is it a good practice?
No but, fuses are cheap compared to large size breakers.


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## AK_sparky (Aug 13, 2013)

I know some prefer to put fuses in mains because it encourages better troubleshooting. It's a lot easier to just flip a breaker back on after "trying something" as a fix; if it's not fixed just try something else and flip the breaker again! With a fuse you tend to make sure you got it fixed.


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## 99cents (Aug 20, 2012)

micromind said:


> This is one of two reasons why I will not install fuses as service equipment. Of course, just about anyone will install the largest possible fuse if one of them blows.
> 
> The other reason is if one of them blows, every 3Ø motor is in serious peril. Even if properly protected.


The fuses might be there to lower the SCCR of downstream equipment. Fuses have their uses. It's difficult to say, "I will not use use fuses on service equipment". What if it's a designed system using fuses?


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## macmikeman (Jan 23, 2007)

99cents said:


> The fuses might be there to lower the SCCR of downstream equipment. Fuses have their uses. It's difficult to say, "I will not use use fuses on service equipment". What if it's a designed system using fuses?


I still run into a healthy amount of service/ distribution equipment that utilizes fuses for that reason.


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## 99cents (Aug 20, 2012)

frank1023 said:


> i have a question on a service i have seen feeding a bank main lug panel.
> 
> the main is a fused 3 phase pullout rated for 200 amps. 1/0 thhn feeding it on the line side and 1/0 feeding it on the load side 70 feet away to the main lug panel. The fuses are 150 amp each. Is this acceptable?
> 
> just curious because if a fuse blows whats stopping a handyman from replacing it with a 200 amp fuse, in that case the wire size is inadequate for the fuse.


The world is not handyman proof. How many times have you seen HRC fuses replaced with 10K's?


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## ponyboy (Nov 18, 2012)

Isn't it true that in canada that disconnects need to be supplied by conductors sized to carry the max current rating on the disconnect for this very reason?


Sent from my iPhone using Tapatalk


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## 99cents (Aug 20, 2012)

ponyboy said:


> Isn't it true that in canada that disconnects need to be supplied by conductors sized to carry the max current rating on the disconnect for this very reason?
> 
> 
> Sent from my iPhone using Tapatalk


Why is this no different than putting a 150 amp main breaker in a 200 amp frame?


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## ponyboy (Nov 18, 2012)

99cents said:


> Why is this no different than putting a 150 amp main breaker in a 200 amp frame?



Not sure what you're asking. I was under the impression that you had say a 60 amp disconnect you HAD to feed it with 60 amps (breaker, wire, everything). I thought I remember seeing that in a Canadian thread


Sent from my iPhone using Tapatalk


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## 99cents (Aug 20, 2012)

ponyboy said:


> Not sure what you're asking. I was under the impression that you had say a 60 amp disconnect you HAD to feed it with 60 amps (breaker, wire, everything). I thought I remember seeing that in a Canadian thread
> 
> 
> Sent from my iPhone using Tapatalk


Nope.


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## telsa (May 22, 2015)

I'll take a WAG that these are T type Service fuses.

Such down sized fusing is done all across America. ( and probably Canada, but that's a guess )

The solution to errant janitors and landlords: spare fuses held in a spare fuses box mounted to the wall or 3R equipment. Such an expense is trivial and keeps the store in business.

Poof. Problem gone.


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## micromind (Aug 11, 2007)

99cents said:


> The fuses might be there to lower the SCCR of downstream equipment. Fuses have their uses. It's difficult to say, "I will not use use fuses on service equipment". What if it's a designed system using fuses?


I haven't seen fuses in series with a breaker on a service......yet........but I have seen it in switchgear. 

The best systems have a blown fuse relay that will shunt-trip the breaker if one or more fuse has voltage across it. 

The main problem I have with these systems is that very few people understand them. I've had more than one frantic call that a breaker won't reset or the breaker is on but one phase is dead. 

I have learned over the years that the simplest design is almost always the best.


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## triden (Jun 13, 2012)

ponyboy said:


> Not sure what you're asking. I was under the impression that you had say a 60 amp disconnect you HAD to feed it with 60 amps (breaker, wire, everything). I thought I remember seeing that in a Canadian thread
> 
> 
> Sent from my iPhone using Tapatalk


No,but we are supposed to place a label on it stating "Max fuse size xxx amps".


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## 99cents (Aug 20, 2012)

triden said:


> No,but we are supposed to place a label on it stating "Max fuse size xxx amps".


Is there a rule for that?


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## triden (Jun 13, 2012)

99cents said:


> Is there a rule for that?


Come to think of it, I'm not sure. Inspector told me that way back and I've always done it. Going to look it up.


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