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PLC program loss

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
An AB 1500 I installed 25 years ago has lost its programming twice in the last month and appears to be associated with a rebar driven into one of the 480 volt Cu feeder conductors. Not a failure but a ground fault. It has been dry since the 1st of September with only two rains. Each program loss coincided with the rain. The rebar caused fault was found during the 2nd rain.

The extremely expensive second PLC battery installed a few years ago has good voltage.

Would a SPD installed on the 1KVA(?) secondary feeding the PLC and associated controls help?
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
ptonsparky said:
Would a SPD installed on the 1KVA(?) secondary feeding the PLC and associated controls help?
Click to expand...
SPDs are for protection against fast rising voltage spikes not surges and definitely not voltage drops, dips, or sags.

A ground fault most likely causes a low voltage condition which is best addressed by a constant voltage source like a UPS.
 
M

ModbusMan

Member
Location
Cleveland, OH
Occupation
Building Automation Engineer
Be aware that adding the UPS will likely require that you power down the PLC, so have a copy of the program (and programming software) handy in case the memory gets lost yet again. Since you're already taking the thing down to add the UPS, I would also add a wrap-around bypass of some kind for when (not if!) the UPS faults. I've used Vertiv's MicroPOD switches a couple of times for this sort of thing, and would think that APC and Tripp-Lite make similar devices. If the UPS you choose uses VRLA batteries (and most small systems will), be sure to mark the in-service date and put those things on a two-year rotation.
 
B

BIN95

Member
Location
Las Vegas NV 89148
Occupation
Instructor
ModbusMan said:
Be aware that adding the UPS will likely require that you power down the PLC, so have a copy of the program (and programming software) handy in case the memory gets lost yet again. Since you're already taking the thing down to add the UPS, I would also add a wrap-around bypass of some kind for when (not if!) the UPS faults. I've used Vertiv's MicroPOD switches a couple of times for this sort of thing, and would think that APC and Tripp-Lite make similar devices. If the UPS you choose uses VRLA batteries (and most small systems will), be sure to mark the in-service date and put those things on a two-year rotation.
Click to expand...
Excellent advice.
 
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