Help with fuses blowing in shaper after installing new phase converter

[Phillip Mitchell]

I am scratching my head here and could use some help / guidance as to how to troubleshoot this. Not an electrician but will attempt to describe and contextualize the situation below. Also posted over on OWWM electrical, fyi.

(2) small fuses in the starter wiring of my Wadkin BEM shaper have blown twice now after installing a new phase converter. It ran fine and long and plenty with the old RPC. The machine has test started fine 2 different times (with original fuses with first start attempt after phase converter swap, then again today after replacing 1st blown fuses with new ones) but then I go back to it an hour + later and nothing…crickets when I push the on switch… and discover the fuses are blown (again.) I have double checked all connections (plug end, inside the starter/contactor/overload box, at the physical switch, etc on machine, at the motor leads connection)…did that first before checking the fuses.

I just installed a new phase converter last week - Phase Perfect 10hp 240v. See photo for some specs below. Happy to elaborate. The old RPC was a Kay rated for 10hp and had the exact same infrastructure (all wiring to and from and 3 PH subpanels, receptacles, etc) as what is here now. The only thing that has changed is the new Phase Perfect vs the old Kay RPC.

Testing the fuses with a simple multimeter (touching each end of removed fuse with each multimeter lead on ohm setting) gives me a reading of “1”.

Fuses are (2) Class CC ATMR 1/2 600 VAC - the replacement was matched exactly (and they were not cheap or able to be sourced locally…)

There is another slightly larger fuse below these in the starter box that is not blowing - Class PK5 1 amp 250 VAC

The overload relay is set to 30 amps, fwiw.

The phase perfect is rated to output more amps compared the old RPC and is certainly much more efficient but I have it’s output going into a 3PH MLO sub panel and on both 20 amp and 30 amp 3 phase breakers with appropriate receptacles for each (the shaper is and has been on a 30 amp receptacle as it is a 27.4 FLA motor @ 220v). This all ran fine multiple times before the phase converter switch. All other machines are running and working fine/great after the phase converter switch.

What is happening here and what do I need to do to get this to work?

[Jeff Bartley]

I’d try calling Phase Perfect. They have some very electric-savy folks that could probably help.

After seeing pics of your set up I kinda wish mi e was mounted outside. I don’t mind the hum but I usually turn it off if I won’t be running machines for a bit.

[Phillip Mitchell]

I’d try calling Phase Perfect. They have some very electric-savy folks that could probably help.

After seeing pics of your set up I kinda wish mi e was mounted outside. I don’t mind the hum but I usually turn it off if I won’t be running machines for a bit.

Thanks Jeff, I will call them tomorrow. You’re right that they may have a simple answer for me. This is certainly above my head and limited electrical knowledge and diagnostic skills.

This is a photo of the Phase Perfect outside install that Jeff is referencing. It’s a NEMA 3R outdoor enclosure.

[Phillip Mitchell]

Talking to Phase Perfect tech support did not really resolve anything. Once I told them the manufactured leg was not going to this transformer/fuses then the only other thing they said was to try and monitor the real time onboard voltage display when starting the shaper and see how much it drops, noting that the lower the voltage drops (momentarily) the higher the current is and it could be overloading the fuse…which would suggest that the phase converter is not large enough to handle this load.

That does not really track with the fact that is started fine before on a less efficient RPC with less balanced voltage and my 9 hp 20” planer with 5” diameter cutter head is starting great with the new converter. I’m not quite sure where to go from here, but I am about to order more fuses (I have none left of this size) and a direct match replacement of the transformer in between these fuses in case something is incidentally going south with the current one and causing issues. So it will likely be mid-late next week before I have the opportunity to trouble shoot again with fresh fuses. They are not available locally as far as I can tell.

[Malcolm McLeod]

…
Fuses are (2) Class CC ATMR 1/2 600 VAC …

Fairly certain these are ‘fast-acting’ fuses, and generally used to protect delicate electronic devices. I am not sure why you’d need such in a motor control circuit ….. unless there are digital displays (or other such ‘lacy delicates’)?

Check the schematic. If this circuit simply feeds the starter coil, I’d replace with either normal duty 1/2A fuses, or perhaps 1/2A ‘slo-blow’.

[Phillip Mitchell]

Fairly certain these are ‘fast-acting’ fuses, and generally used to protect delicate electronic devices. I am not sure why you’d need such in a motor control circuit ….. unless there are digital displays (or other such ‘lacy delicates’)?

Check the schematic. If this circuit simply feeds the starter coil, I’d replace with either normal duty 1/2A fuses, or perhaps 1/2A ‘slo-blow’.

Yes, the originals along with the replacements I sourced are “fast-acting”. I don’t know if this makes any difference as to what type of fuse would be appropriate, but the control circuit does have an analog ammeter mixed in with the on/off switch and forward/neutral/reverse switch. See photo.

I’m confused about the fast acting vs time delay - the shaper started and ran (for test starts) a couple of different times on each set of fuses initially and I typically let it run for several seconds before shutting it off. Then when I came back to it hours/days later was when it there were crickets and it was blown. Wouldn’t the “fast-acting” fuse blow immediately and not start and run a couple of times initially if too much current was incoming consistently?

This is post Phase Perfect install, to be clear. This was never a problem with the old Kay RPC.

Thank you for the reply, by the way.

[Bill Dufour]

Looks like all you have is a analog meter. Use slow blow or motor rated fuses. No eelctronics to protect so no need for fast blow fuses. It may be cheaper to replace the fuses with copper wire jumpers and add an external breaker box.
Fast blow fuses are like any other fuse. they blow once and never reset.
Slow blow, time delay, motor fuses take a few seconds to warmup enough to blow. Long enough for a motor inrush currentt to pass on startup before blowing. On a dead short they blow as fast as anything. Just take longer on slight overloads.
A motor can easily draw 400% of full load amps on startup for 2-3 seconds.
Bill D.

[Bill Dufour]

I do not see the need for any fuses except maybe the low amp control fuses. The switch or contactor has overloads built in. Modern NEC allows a VFD to be considered a disconnect switch. That might require a maintained off switch or a breaker turned off as well. Not really sure .
Bill D

[Malcolm McLeod]

Spared from seeing pics (a ‘perk’ for members).

Sounds like the 2 problem fuses are there to protect the input to a control power transformer (with the 1A fuse protecting the output). There is no reason I can think of for them to be ‘fast-blow’. I’d swap to standard duty or even ‘slow-blow’ in same amperage ($3-4?).

If you think issue will be on-going and you’ll blow them on a weekly basis, then Mr. Dufour’s idea of a breaker might be convenient & economical in the long run. You can pull the fuse holder(s) and replace with a 2-pole breaker, but that will likely cost $50-60. (No need to mount it externally and I’d stay away from 2-pole household CBs, even if you could find one in 1/2A. rating.)

Caveat: I’m not a 3-phase conversion user, so can’t explain the PP vs Kay performance, but sounds like PP is throwing some current/voltage spike as load drops. I suspect it would take an oscilloscope to capture it.