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#113669 - 09/13/02 10:11 PM Topic: >> Over-Fused Panel
Admin Online   content

Registered: 10/07/00
Posts: 3188
Loc: NY, USA
Assume that the following is the Service Panelboard found in a Home. What are the problems and concerns? Code Violations, Solutions?

I believe this image was from the archive of Redwood Kardon
Tools for Electricians:
#113670 - 09/14/02 04:09 AM Re: Topic: >> Over-Fused Panel
sparky Offline
Registered: 10/18/00
Posts: 5545
This i see daily, green is usually a trade standard for a 30 A fuse, and as most older wiring is 14 or 12 gauge, one look says it all.

the circuitry supported the dwelling originally, but it did not get upgraded as our electrical addiction grew.

someone simply inserted a higher amp fuse, so now the fuse is
in the circuit, which was it's primary job.....

onto the NEC...


from 240.4 (D)....

(D) Small Conductors. Unless specifically permitted in 240.4(E) through (G), the overcurrent protection shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.
#113671 - 09/14/02 06:56 AM Re: Topic: >> Over-Fused Panel
Bill Addiss Offline
Registered: 10/07/00
Posts: 4196
Loc: NY, USA
in the circuit, which was it's primary job.....

I like the way it sounds, but is it technically true? Perhaps modified to 'May no longer be .." would be more accurate.

What are the dangers here? What will happen?


[This message has been edited by Bill Addiss (edited 09-14-2002).]
#113672 - 09/14/02 11:41 AM Re: Topic: >> Over-Fused Panel
HotLine1 Offline

Registered: 04/03/02
Posts: 6833
Loc: Brick, NJ USA
The dangerous conditions are:
The branch circuit conductors are "overfused", which could cause overheating (if it hasn't already)
Overheating causes insulation deterioration.
Insulation deterioration leads to "shorts"
Shorts can lead to fires.

How many times have some of us found old splices that were "crispy critters"; touch it & the insulation crumbles in your fingers.
Fusestats most of the time cure the overfusing, until the occupant figures a way to defeat the rejection mech.
In this case, the fuses are "not the weakest links". The old #14 will be.

#113673 - 09/14/02 11:50 AM Re: Topic: >> Over-Fused Panel
sparky66wv Offline
Registered: 11/17/00
Posts: 2342
Loc: West Virginia
More importantly, the splices and/or terminations will most likely be the weakest link...

I guess we do need a slight disclaimer, even properly sized fuses cannot be guaranteed to be the weakest link.

Have Bill and I sufficiently torn you apart now Steve?

Residential/Commercial Inspector
5 Star Inspections
Member IAEI
#113674 - 09/14/02 05:21 PM Re: Topic: >> Over-Fused Panel
sparky Offline
Registered: 10/18/00
Posts: 5545
that's ok Virgil,
the threads 'end' justifies the means,
#113675 - 09/17/02 05:22 PM Re: Topic: >> Over-Fused Panel
John Steinke Offline
Registered: 04/03/01
Posts: 509
Loc: Reno,Nv., USA
This is one reason why I like those plug-fuse shaped circuit breakers- it's a lot easier to reset, thereby avoiding a trip to the hardware store (where you'll be tempted to get a bigger fuse!).
Here is one area wher I think the code could be better worded & arranged (240-50 thru 54).
As presented, "plug fuses" are OK everywhere, while "Edison-base fuses" are tamper resistant, but only to be used where there is no evidence of overfusing; yet, their different-sized bases are designed to prevent over-fusing. Why require them where they're not needed?
I have often been told that this mess means that I'm required to put type 'S' adapters into plug fuse sockets whenever I encounter them. I am further told that, since the fuse-shaped circuit breakers are "full" sized (as compared to type 'S'), that I therefore am not allowed to use them!
It has been my observation that, after a few trips to re-set the breaker, people generally figure out that it's not a good idea to run the microwave and the breadmaker off the same outlet, at the same time, and modify their behaviour accordingly. These same people will also quite happily buy a 30-amp fuse, and persist in bad habits.
I think that a closer look at the use of these over-fused circuits would show them to be only moderately overloaded, for only a relatively short period. One advantage to CB's is that they respond in relation to the length as well as the size of the overload. Maybe our quest for "more safety" has resulted in "no safety, as the consumer cleverly goes around us.
I submit that these are tha same homes that are filled with extension cords, plug adapters, flying splices, and myriad other problems. Maybe the over-fusing is but a symptom of a senile wiring system.
#113676 - 09/18/02 07:25 AM Re: Topic: >> Over-Fused Panel
mamills Offline
Registered: 11/30/01
Posts: 739
Loc: Wharton, Texas, USA
I ran into this kind of overfusing situation a few years back while visiting an aunt(well into her 80's) in North Carolina. She lived in a c.1920's two story house with K & T wiring and one of those "main + range + 4" fuse panels which were/are so prevalent. She had just installed three new window air conditioners upstairs, then began having problems blowing out fuses (one fuse for the entire second floor). While visitng, and on the first of many trips to the fuse box while I was there, I noticed that all the plug fuses were 30's (big surprise...). Examining the inside of the box, as well as the visible wiring in the attic, revealed No. 12, and in a few cases, No. 14 awg conductors, most of which were in pretty dicey condition. After explaining to her that she and her house were both living off borrowed time like this, she needed to use smaller fuses until she hired an electrician to do a complete rewiring for her. She became extremely angered by the fact that I replaced the oversized fuses with 15's, explaining to me in no uncertain terms that "the 30's don't blow out anywhere near as fast as the smaller ones, plus they all cost the same and you're just wasting your money".

If you're looking for a weak link here, I would dare to say that it's her appalling lack of education (not that I hadn't tried many times since that visit to set her straight). If there's an up-side to all this, I guess it would be that she finally had the house rewired recently - thanks to a weak splice that finally burned in two and rendered most of the upstairs without power (and without a resulting fire, thank God).

Mike (mamills)

BTW; the electrician removed the box intact and my aunt sent it to me, so I ended up with a nice "new" fuse box for my collection!

[This message has been edited by mamills (edited 09-18-2002).]
#113677 - 09/18/02 09:55 AM Re: Topic: >> Over-Fused Panel
Joe Tedesco Offline
Registered: 10/07/00
Posts: 3325
Loc: Boston, Massachusetts USA

The picture of the oversized green fuses did come from Redwood's online archive, which was where I too had many of my images stored.

He is currently working on a remodel of his web site, and may include some, if not all of our images.

The images were posted in the Public Domain, and your note is a courtesy to Redwood.

If I was to receive an email from the many who use my images in their seminars, and for training or fun, I would be happy to reply giving my approval.

Some of the IAEI, UL, OSHA, and other groups use them, that's what they are for!

I will copy Redwood so he can come back with his comments, if necessary.
Joe Tedesco, NEC Consultant
#113678 - 09/18/02 11:27 AM Re: Topic: >> Over-Fused Panel
pauluk Offline
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England

That sounds very much the quote here in England where somebody said that if they were in any doubt about what size fuse to use they'd use the largest available.

"It would be safer because there's less chance of it blowing."


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