Surge protection devices 1

[Indy]

Hi,
We have a contractor that is supplying a level switch. It has been suggested that we should consider surge protection local to the switch. My question is would it not be better to install the surge protection device at the switchboard suppling the level switch?


Thanks

 

[Skogsgurra]

Yes. If you want to supress fast transients caused by switch opening (or bouncing), it works just as well anywhere in the circuit. Many guys says that it is better to supress "at the source". Not true in many cases, including this.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[djs]

You have to realize what you want protected. In general a simple contact will survive a lot of gruff and will not need protecting. What that switch is connected to is usually not as robust and does need protecting. The surge suppressor needs to be mounted as close as possible to the device being protected.

 

[ScottyUK]

There is some logic to 'suppressing at source' if there is the possibility of capacitive or inductive coupling into other parallel circuits, for example on a multicore cable where it is better to prevent the coupling occurring rather than deal with it once it is where it shouldn't be. Equally there are arguments in favour of suppressing at the sensitive load, where there are multiple possible interfering sources or where the source is something like a lightning strike which can't readily be suppressed. As with most problems, there's no cut & dried simple answer other than 'it depends'.

 

[itsmoked]

The major method of suppressing spikes is to consume them somewhere other than in the sensitive device or devices being protected. If you put the suppressor at the location the spike is being generated there is little resistance for the spike suppressor to work with. This means just about ALL the consumed energy is going to have to dissipate in the protection device. This stresses the protection device and can lead to its rapid failure and then there's nothing protecting the sensitive devices the next time around. It's much more effective to put the protective device way down the conductors leading to the-device-to-be-protected so when the protection operates the energy that needs to be dissipated can be spread all the way down the conductor's resistance.

The only negative of this placement is what Scotty describes above. You need to seek a useful balance somehow. Possibly using multiple protection devices.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[cranky108]

Years ago, prior to modern MOV's they used despiking capacitors in DC controls, and free wheeling diodes across coils.

Now the MOV in the circuit. Sort of depends on the type of spike, or noise.

 

[Skogsgurra]

You don't seem to get it. If you use a snubber at the receiving end - then there will not be any problems at the switch end or the receiver. The transients are killed by the RC snubber AND the cable capacitance. So, there's nothing happening at all. Except the contact closing and opening quietly.

I did show a few examples of this last year. I'll look for it. It is somewhere on EngTips.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[VEBill]

In situations like this, it's worth being cautious to ensure that the cost of the decision making doesn't exceed the cost of simply (mindlessly) installing surge protection at both ends.

Who hasn't been in lengthy $1k/hour meetings discussing $10 'This-Or-That' decisions?

(Mentioned only because nobody else would... )

 

[waross]

We had an issue with a control transformer when the supplied fuse would not hold the energization inrush.
We lost about 3 fuses before installing a suitable fuse rather than replacing another OEM fuse.
The next day my boss got a call from the owner of the company that we were subbing to, blaming our electrician and demanding that we pay the cost of the replacement fuse.
I overheard the call and pulled out a catalogue and underline the fused in question.
My boss to me:
"Is that the fuse that was installed?"
"Yes"
To complainer;
"Uh, you know, that fuse retails for $0.20."
Silence.
End of call.
I hear you VE1BLL.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[djs]

I once had a project where the EoR specified interposing relays of the discrete outputs and then also surge suppressors on the relay contacts. So ended up with a $65 surge suppressor protecting a $5 relay!

 

[itsmoked]

$65 surge suppressor protecting a $5 relay

Often worth it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

We have a contractor that is supplying a level switch.

Is this a simple switch or a level transmitter?

Bill
--------------------
"Why not the best?"
Jimmy Carter