Plug fuses/interpretation?

[Glennwith2ns]

Awhile ago I asked this question and I would like to ask it again in a different way.


240.50 Plug fuses

(A) Max. Voltage

Plug fuses shall be permitted to be used in the following circuits:

(1) circuits not exceeding 125 volts between conductors.

(2) circuits supplied by a system having a grounded neutral where the line-to-neutral voltage does not exceed 150 volts.


Feeding a typical 220 volt line in a residential application to a 2-fuse disconnect would seem to comply with no.(2) but not with no.(1).

Is this a situation where one or both rules must apply and where would this be stated in the codebook?

I also note with interest 240-60 Cartridge fuses:


(A) Max voltage

Cartridge fuses and fuseholders of the 300 volt type shall be permitted to be used in the following circuits.

(1) circuits not exceeding 300 volts between conductors

Why plug fuses limited to 125 volts and cartridge fuses 300 volts??

Glenn

 

[bphgravity]

Re: Plug fuses/interpretation?

I believe that 240.50(A)(1) is for 120/240 single phase systems, and (2) is for 208Y/120 3-phase systems. As far as why cartridge fuses are allowed on systems of 300-volts and plug fuses are only allowed to 150-volts, it probably comes down to listing and testing of these type of fuses. It may not be possible for a manufacturer to make a 300-volt capable plug fuse? I have no technical data or substantial proof. Just my interpretation of the articles.

 

[Glennwith2ns]

Re: Plug fuses/interpretation?

Let me ask it this way,

If you wired a 220 volt line to a water pump at someones house through a 2-plug fuseholder disconnect, would you not be in violation of 240-50(A)(1)??

 

[bphgravity]

Re: Plug fuses/interpretation?

No, I was in error with my first post, both 120/240 single phase and 208Y/120 three phase meet the requirement of (2) I think the (1) might be for vintage sytems that are non-existant any longer. Even though the 220-volt line to line voltage exceeds, (2) allows the installation because line to neutral does not exceed. I believe (2) used to be an exception to (1), I do not know why they have made it so confusing now?

 

[frenchelectrican]

Re: Plug fuses/interpretation?

yeah but one instering part about plug fuse is not listed for delta service you have to rember the wild leg ( i don't care what you call it ) it will crank out anywhere from 190 to 208 volts and by nec codes and plugs fuse are only rated for 150 volts but for catrage fuse they are rated for 300 volts from line to ground and it is possible to use on 277 volts system on single phase only but when go with three phase it is diffrent matter to deal and they have 600 volts catrge fuses but never the plugs at all

merci marc

 

[charlie]

Re: Plug fuses/interpretation?

Feeding a typical 220 volt line in a residential application to a 2-fuse disconnect would seem to comply with no.(2) but not with no.(1).

Glenn, I don't know about you but I found everyone's answers a little confusing. To directly answer your question, the typical 120 or 240 volt line will work with standard Type S fuses in a residential application. The statement is "Plug fuses shall be permitted to be used in the following circuits"

 

[russ]

Re: Plug fuses/interpretation?

I was trying to find a way to respond to this question.
Besides whats allready been said, 240.20(B) is specific about circuit breakers opening all ungrounded conductors. I would assume fuses don't have the same requirement, because their not mentioned.

Russ

 

[gserve]

Re: Plug fuses/interpretation?

I would not wire a 240V circuit to 2 separate plug fuses they are for 120V circuits. You would have to unscrew both fuses to turn power off. This may be a code violation. Kinda like putting 2 single pole breakers for a dryer application that requires a double pole breaker to disconnect both ungrounded conductors at the same time.

 

[bennie]

Re: Plug fuses/interpretation?

There is many services with a fused pull out main.

 

[renosteinke]

Re: Plug fuses/interpretation?

The code is attempting to itself comply with what was once the standard panel- the "fuse box."
In the pre-CB days, homes had fuse boxes. The 220 circuits had fuses in holders that removed both fuses at once; the 110 circuits had screw-in "plug" fuses.
As with knob & tube wiring, these panels are no longer allowed in new construction.

 

[russ]

Re: Plug fuses/interpretation?

I'll grant that fuse boxes aren't installed anymore but I don't know of any code refrence that says it illegal with Stat type fuses. Circuit breakers may be more convenient, but their not as quick to react In my opinion.

Russ

[ March 27, 2003, 08:16 PM: Message edited by: russ ]