Subject: Re: [Shop-talk] Mixed fuse sizes?

From: John Innis <[email-masked]>
Date: Fri, 29 Aug 2014 14:34:12 -0500

I have seen this before, but ONLY when the "240 V" circuit was being used
as two separate 120V branches.  So house originally had a 240v water
heater, it was replaced with a gas water heater and the now unused 204v
circuit was re-purposed into two 120vac branches.  I am pretty sure this is
not to code, and generally not a good idea.  As soon as you have a single
240v load back on that circuit, you need to go back to matching fuses.  The
cartridge style fuses always look burned when they blow, but this one
likely was running on the ragged edge for a LONG time.  Ideally you need to
install TWO new 50amp fuses in this fuse carrier.  But Not sure if they are
available in that rating.  More important, you need to find out if anything
else is wired to that circuit.  If someone installed a branch circuit with
14 ga wiring, it MUST be disconnected from this circuit, it will not
survive the 50 amp load in the event of a short.

On Fri, Aug 29, 2014 at 2:12 PM, Jim Stone <[email-masked]> wrote:

> A friend of mine called me last night with an electrical question that I
> couldn t answer, so I am turning to this group.  His 240v electric stove
> petered out on him the previous night.  The heat output gradually declined
> until it just stopped working.  He checked the fuse and discovered
> something I
> have never heard of before: mixed amperage Buss fuses in a single carrier.
> The house is old and the fuse box has never been updated, so he has
> screw-in
> fuses for the 120 circuits and the push-in Buss type (I don t know the
> proper
> name) for the 240 circuits.  When he pulled the carrier (don t know the
> name
> for that either) for the stove he found that it contained one 30 amp fuse
> and
> one 60 amp.  The 30 amp fuse has an adaptor to allow it to fit into the 60
> amp
> carrier.  The owner s manual calls for a 50 amp circuit, so I guess it
> averages out about right.  I posted a photo of the holder here
> (http://tinyurl.com/k47qq6h) and the new fuse with adaptor here
> (http://tinyurl.com/lknxn4f), if anyone is interested.  The 30 amp fuse
> had
> blown and looked burned to him.
>
> I have never heard of mixing two different fuses in the same circuit, but
> the
> stove was professionally installed and has worked fine for 10 years.  The
> fuses were much older than that, so the electrician clearly used an
> existing
> circuit for wiring the stove.  It is labeled  Water Heater , although the
> house didn t have an electric water heater when he bought it. He can
> certainly
> just leave everything the way it was and put in a new 30 amp fuse, but that
> makes him, and me, uncomfortable.  Can anyone shed any light on why this
> might
> have been done and what he should do now?
>
> Thanks.
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From: Jim Stone <[email-masked]>
Date: Fri, 29 Aug 2014 15:43:30 -0400

Thanks, John.  That is pretty much what I assumed, although I didnt think
about the fact that there might be a branch circuit in there somewhere.  Good
catch!  One thing I forgot to mention is that they were slow blow fuses.  I
believe that is appropriate for a stove, but could be disaster on any branch
circuit.

Home Depot lists 50 amp fuses, so hopefully they are readily available.  I
assume he will also have to find a matching carrier or proper adapter, but
that should be possible given that the fuses are out there.

I will pass this info on to my friend.  When he called last night I told him I
didnt have a definitive answer, but knew right where to find one!  Thanks for
the quick response and for proving me right.

Jim

On Aug 29, 2014, at 3:34 PM, John Innis <[email-masked]> wrote:

> I have seen this before, but ONLY when the "240 V" circuit was being used as
two separate 120V branches.  So house originally had a 240v water heater, it
was replaced with a gas water heater and the now unused 204v circuit was
re-purposed into two 120vac branches.  I am pretty sure this is not to code,
and generally not a good idea.  As soon as you have a single 240v load back on
that circuit, you need to go back to matching fuses.  The cartridge style
fuses always look burned when they blow, but this one likely was running on
the ragged edge for a LONG time.  Ideally you need to install TWO new 50amp
fuses in this fuse carrier.  But Not sure if they are available in that
rating.  More important, you need to find out if anything else is wired to
that circuit.  If someone installed a branch circuit with 14 ga wiring, it
MUST be disconnected from this circuit, it will not survive the 50 amp load in
the event of a short.
> until it just stopped working.  He checked the fuse and discovered something
I
screw-in
proper
name
and
amp
> (http://tinyurl.com/lknxn4f), if anyone is interested.  The 30 amp fuse had
the
existing
certainly
might

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