UTS6H Fuse Question

[erikd_apc]

This was originally posted on APC forums on 9/9/2013

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I have an UTS6H installed in my home.  My question is regarding the fuses used in the UTS.  Twice I've had to replace a fuse on a circuit, once because of a frayed vacuum cleaner cord and the other time after a light bulb burnt out.  Both times the fuse inside the UTS blew before the circuit breaker in my main panel tripped.  This is a huge inconvenience having to remove the UTS cover to service the fuse.  Not to mention these fuses are very expensive $15+ each??

My first question is why are these fuses in series while on Utility power?  I'm assuming they are present to protect the circuit while on generator power.

2. Why were fuses chosen and not resettable circuit breakers for this design?

3. Is there an easy way to convert these fuses to circuit breakers?

[erikd_apc]

This was originally posted on APC forums on 9/9/2013

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I have an UTS6H installed in my home.  My question is regarding the fuses used in the UTS.  Twice I've had to replace a fuse on a circuit, once because of a frayed vacuum cleaner cord and the other time after a light bulb burnt out.  Both times the fuse inside the UTS blew before the circuit breaker in my main panel tripped.  This is a huge inconvenience having to remove the UTS cover to service the fuse.  Not to mention these fuses are very expensive $15+ each??

My first question is why are these fuses in series while on Utility power?  I'm assuming they are present to protect the circuit while on generator power.

2. Why were fuses chosen and not resettable circuit breakers for this design?

3. Is there an easy way to convert these fuses to circuit breakers?

[BillP]

This reply was originally posted by Secret on APC forums on 9/10/2013

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Hi erikd,

The UTS panel itself was designed to be placed in series between the Service panel and the Load for ease of use/installation, as well as additional functional benefits found in the UTS, i.e. Security Mode, Electrical Phase Status, etc.

Fuses were also chosen for specific reasons. Fuses are known to have a much more exact tripping point and faster response time than that of the typical circuit breaker. In addition, circuit breakers are designed to be tripped no more than 2-3 times as a result of a fault interruption, before requiring replacement. While the UTS fuses are easily replaceable in the field, miniature circuit breakers would require hard wiring to the UTS panel and involve extensive manipulation of the panel to replace these breakers. The UTS is considered a self contained electronic device, therefore the replaceable circuit breakers used in electrical service panels could not be used.

Although there is no way to convert the unit to circuit breakers, we have included a series of Male to Male fast-tons which would allow for by-pass of the fuse function if a fuse were to blow and no replacement fuse was available. This would enable the enduser/installer to reapply power to the circuit until a fuse could be acquired.

FYI; the Male to Male fast-tons are for use as a temporary repair and are not intended for continued use in place of the fuse.

SecretSquirrel

[erikd_apc]

This was originally posted on APC forums on 9/10/2013

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Thanks for the reply.

I think that's my point.  Fuses are known to have a much more exact tripping point.  They will open before a circuit breaker will trip in many cases.  This effectively reverts my 6 circuits back to the 1940's, fumbling around in the dark trying to replace a fuse that has blow.  Which was the case just this past weekend when a night light bulb (believe it or not) that had burnt out rather violently and took out a fuse in the UTS.  Here's pic of the bulb.  You can see one electrode had actually melted.

If code will not allow the use of electrical service panel breakers in the UTS then I would suggest changing the design so that the fuse is not in the circuit while on utility power.  The fuse is only needed while on generator or UPS power.  This would eliminate these nuisance fuse replacements 99% of time.

[BillP]

This reply was originally posted by E. on APC forums on 9/13/2013

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Is this also the case in "Bypass" mode?  Are the fuses in line with the load then?

[erikd_apc]

This was originally posted on APC forums on 9/16/2013

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Yes, I believe so.  The fuses are always in line.  That would have been convenient option to re-energize a circuit with a blown fuse, to simply place that circuit in by-pass.  But based on the current design that would have required another bank of relays.  I believe By-Pass mode simply disables all UTS functions for that circuit but doesn't actually "by-pass" the UTS.

[elec-engr_apc]

This was originally posted on APC forums on 9/22/2013

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The Ferraz Shawmut fuses are $7.88 each at Zoro Tools, not cheap but better than list price. I keep several spare 15's and 20's just in case.

However, I have had my UTS10BI for over a year and haven't blown a fuse yet. When my wife uses her hair dryer on full blast, that circuit occasionally overloads. It always trips the overcurrent sensor in the UTS first, which shuts down the circuit. All I have to do is follow the instructions on the UTS display (basically just press any button on the UTS) to reset it, and it comes right back on. I have even trained my wife to do this in case I'm not there. I have also recommended that she not use the "high heat" setting on her hair dryer 😉

This is a 15 amp circuit, on a 15 amp breaker, set to a circuit amp rating of 15 amps in the UTS setup and with a 15 amp fuse in the UTS. And the UTS overcurrent sensor is always (at least so far) the first to trip, which is obviously better than blowing the fuse. Perhaps your overloads (i.e. blown light bulb) have been a little more "violent" than mine and that triggers the fuse first. In any event, you may want to double-check your UTS setup to make sure the circuit amp rating matches the UTS fuse as well as the circuit breaker.

[PeteCress_apc · Accepted solution]

This was originally posted on APC forums on 9/22/2013

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You are not alone with the night light's blowing a fuse in the UTS-6.

Happened to us last night - with the little extra twist of "Someone" just telling me that the lights in 2 bedrooms "stopped working"..... after about an hour of pulling the main breaker panel, pulling the cover on the UTS-6 and generally fooling around, it emerged that the "stopped working" was conincident with her night light making a flash and a noise..... -)

Must be something with those night light bulbs.

I note that all the fuses on my UTS-6 are fast-blow.   Do they have to be fast-blow?   Or will slow-blow work?

[erikd_apc]

This was originally posted on APC forums on 9/23/2013

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I suspect the built-in over current sense protection is not designed for arc fault detection.  That too would also be an improvement in the design.  The relatively slow heating of an over current fault is quite different from that of a short circuit arc in terms of over current protection.  Don't get me wrong.  I really like this transfer switch idea and it worked beautifully during our last multi-day outage event but I'm just not thrilled about this fuse design.  I'll probably just change my two general lighting circuits to the slow blow ATDR series fuse and hope that time delay will absorb a light bulb burning out.

[erikd_apc]

This was originally posted on APC forums on 9/23/2013

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That's amusing!  I can't believe someone else experienced this same situation!  Thanks for sharing.