by spec i must supply surge protection for each individual PLC input in my panel. These devices are all of the voltage free (dry contact type) where the 120VAC will be supplied by my panel. i found a WAGO MOV to ground terminal block and i believe this is the appropriate device to comply with the spec and protect my PLC input card from voltage transients. Has anyone used these devices before? Thanks for any help.
surge protection for 120VAC discrete input card
- Thread starter alw_off
- Start date
We use MOVs for protection on some inductive devices, generally not on PLC input circuits.
I'm not sure that a "spike" or "surge" is at all likely from a contact driving an input, but someone writing the spec has somehow gotten ahold of this idea, so now your compliance is required. Yes, the MOV would protect the input. I might prefer connecting it to Input Common rather than to ground, but I guess I have no scientific argument for that, just electrically closer to the actual target. I'm interested in what prompted this spec to be asserted. It's a non-standard practice as far as I know.
I'm not sure that a "spike" or "surge" is at all likely from a contact driving an input, but someone writing the spec has somehow gotten ahold of this idea, so now your compliance is required. Yes, the MOV would protect the input. I might prefer connecting it to Input Common rather than to ground, but I guess I have no scientific argument for that, just electrically closer to the actual target. I'm interested in what prompted this spec to be asserted. It's a non-standard practice as far as I know.
Hi cidchase. i will have some inductive loads as outputs so thanks for the reply. in the case of protecting my PLC inputs I did find a 2 tier MOV that would allow connection to neutral but i thought a connection to ground was more appropriate because the neutral does not leave the panel. Regarding the spec i have seen this as a requirement in specs maybe 10 times so not common but not unheard of. In a lot of cases the spec will say something like 'any signal that leaves the building needs to be surge protected'.
GaryS
Member
I use then usually on outputs some solenoids and contactors coils can have a large collapsing field spike when turned off.
but the best place to install them is across the source ( Coil )
the closer tot he source the better
but the best place to install them is across the source ( Coil )
the closer tot he source the better
hi garys
thanks for the reply. understood regarding placement of MOV. i will have to control motor starters and i agree the best location for a surge suppression device is at the starter. but i also have to build a panel that complies with the spec so even though the correct location is at the starter i will also have to include these devices in my panel. perhaps the engineer is directing me to include surge suppression devices at my end for a lightning strike?
thanks for the reply. understood regarding placement of MOV. i will have to control motor starters and i agree the best location for a surge suppression device is at the starter. but i also have to build a panel that complies with the spec so even though the correct location is at the starter i will also have to include these devices in my panel. perhaps the engineer is directing me to include surge suppression devices at my end for a lightning strike?
Jim3846
Member
You can use fused terminal blocks. Where the fuse is inside the connection bar and they mount on din rail.
GaryS
Member
the first thing is what exactly dos the spec's say
and what are you trying to protect
normally the MOV would be across the coil Hot - natural going to ground would be the second choice.
i like to have everything entering or leaving a panel to terminate on a terminal block
that would be place to put an MOV but that would require 2 terminals for every connections
as for using an MOV for lightning protection / suppression that's just never going to happen the energy that need to be dissipated is way more the any MOV can handle
they would be vaporized instantly. if you need lightning protection then you need a special device
and what are you trying to protect
normally the MOV would be across the coil Hot - natural going to ground would be the second choice.
i like to have everything entering or leaving a panel to terminate on a terminal block
that would be place to put an MOV but that would require 2 terminals for every connections
as for using an MOV for lightning protection / suppression that's just never going to happen the energy that need to be dissipated is way more the any MOV can handle
they would be vaporized instantly. if you need lightning protection then you need a special device
excerpt from spec:
"The Contractor shall furnish and install transient suppression devices for all electrical
(copper) connections providing a direct path to the equipment from outside the cabinet, including CAT 5E cabling from the camera, power, and communications cabling"
My opinion is "equipment" = PLC = ethernet switches = comm cards.
i have seen many municipal wastewater specs where they mandate that any device located in another building or outside be equipped with surge suppression. i am pretty sure this language is there to protect equipment from lightning strikes.
"The Contractor shall furnish and install transient suppression devices for all electrical
(copper) connections providing a direct path to the equipment from outside the cabinet, including CAT 5E cabling from the camera, power, and communications cabling"
My opinion is "equipment" = PLC = ethernet switches = comm cards.
i have seen many municipal wastewater specs where they mandate that any device located in another building or outside be equipped with surge suppression. i am pretty sure this language is there to protect equipment from lightning strikes.
GaryS
Member
Nobody can give to a guarantee protection from lightning
if they really want every input and output protected I hope they have an unlimited budget
you can get surge suppressors for Ethernet and power.
I would install the lighting suppression on the feeder outside the panel so when it blows their will be little damage to the panel.
I have seen many lightning suppressors completely blow up on a strike.
if they really want every input and output protected I hope they have an unlimited budget
you can get surge suppressors for Ethernet and power.
I would install the lighting suppression on the feeder outside the panel so when it blows their will be little damage to the panel.
I have seen many lightning suppressors completely blow up on a strike.
agreed. its tough to try to guess what is intended in these specs sometimes it easy peasy they tell you to use an AB PLC and you comply by using an AB PLC but others the wording is odd or there is a clear contradiction....i think its time to write the dreaded RFI and ask exactly what the engineer is after here. They already mandated a TVSS on the 120VAC power coming in so and they supplied specs i could meet so that is already covered.
Bit_Bucket_07
Member
We use MOVs for protection on some inductive devices, generally not on PLC input circuits.
I'm not sure that a "spike" or "surge" is at all likely from a contact driving an input, but someone writing the spec has somehow gotten ahold of this idea, so now your compliance is required.
...
I'm interested in what prompted this spec to be asserted. It's a non-standard practice as far as I know.
Yes, I've definitely seen inputs damaged by (for example) limit switch input circuits. This can be caused by lightning or short circuits inside of conduits.
I remember one plant in particular that had 480 VAC wiring pulled in the same conduits with 120 VAC control wiring, and the owner had us install surge protection on all PLC inputs and outputs to limit the damage that was caused when a short occurred inside a conduit. It was a limestone plant, and the dust and vibration eventually wears through the insulation of the wires inside of the conduits. It was a major undertaking to install so many surge suppressors.
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