600 volt, 3 phase surge protection

[controlled]

I have a customer with a less than 1 year old rooftop HVAC unit. I havent seen it, but they tell me the FLA of the unit is 22amps at 575 volt. In the last few months, they have lost 3 circuit boards in the unit. I was not part of any troubleshooting, not have i ever seen the unit. The manufacturer is telling them that it must be voltage surges that is causing the boards to go bad.

They want me to recommend and install a surge protector for them.

I have never done any work with surge protectors. Would it be best to install a protector in the load center (protecting the whole panel), or should I install it at the HVAC unit (parallelling the fused isolation switch with another fused switch feeding the protector)?

 

[kwired]

Does this board have lower voltage logic and control devices (guessing it does)?

Maybe a control voltage of 24 volts. What is actual control voltage? Do you know what component is failing on the boards? Make sure you don't have a voltage selector that is set for wrong voltage or are using a wrong tap on a control power transformer. Do you have similar problems with other similar equipment? Surges on the line will appear everywhere on the line, some equipment has surge protection built into it but is still wise to have some external protection.

 

[petersonra]

I have a customer with a less than 1 year old rooftop HVAC unit. I havent seen it, but they tell me the FLA of the unit is 22amps at 575 volt. In the last few months, they have lost 3 circuit boards in the unit. I was not part of any troubleshooting, not have i ever seen the unit. The manufacturer is telling them that it must be voltage surges that is causing the boards to go bad.

They want me to recommend and install a surge protector for them.

I have never done any work with surge protectors. Would it be best to install a protector in the load center (protecting the whole panel), or should I install it at the HVAC unit (parallelling the fused isolation switch with another fused switch feeding the protector)?

I don't see any reason to add a fused switch for the SPD.

There are a bunch of SPD devices out there. I would just go to your local electrical supply house and get whatever they stock that is a type 2 or 3 SPD that can be installed at the unit downstream of the disconnect. Bussman came in last week and showed us some nice DIN rail mounted devices.

I would not be real offended if you put one at the service panel as well. That would be a type 1. If one device is having issues, it seems likely that others might as well.

However, the chances of the problem being surges and thus being solved by any SPD is limited IMO.

 

[controlled]

I don't see any reason to add a fused switch for the SPD.

There are a bunch of SPD devices out there. I would just go to your local electrical supply house and get whatever they stock that is a type 2 or 3 SPD that can be installed at the unit downstream of the disconnect. Bussman came in last week and showed us some nice DIN rail mounted devices.

I would not be real offended if you put one at the service panel as well. That would be a type 1. If one device is having issues, it seems likely that others might as well.

However, the chances of the problem being surges and thus being solved by any SPD is limited IMO.

The reason i mentioned a seperate fused disconnect was because all the protectors I have seen while googling show them being installed in a load center, and require a 30a breaker.

Are the bussman devices series wired? (Meaning the 3 line wires going from existing isolation switch, through bussman devices, then to HVAC unit)

 

[petersonra]

The reason i mentioned a seperate fused disconnect was because all the protectors I have seen while googling show them being installed in a load center, and require a 30a breaker.

Are the bussman devices series wired? (Meaning the 3 line wires going from existing isolation switch, through bussman devices, then to HVAC unit)

If you have 22 FLA, you are probably on a 30A fuse anyway. I personally am not a big fan of adding OCPD that is just for the SPD. If it opens, you will have no SPD but won't know it. None of the Bussman diagrams I looked at showed any OCPD at all. i will send an email to the Bussman guy and ask specifically.

Most SPDs wire in parallel to the load. Some do have feed thru terminals but they are just for convenience.

I personally do not think it makes all that much difference what brand you buy.

 

[petersonra]

I got a response from Bussman the other day and neglected to post it.

The best practice would be to install an SPD on both ends, load center and the HVAC unit to protect surges impacting the circuit boards from both ends. Furthermore, All Type 2 SPDs require an OCPD ahead of them somewhere in the circuit per NEC 285.24. However, no additional OCPD is required for Bussmann BSP UL and Low Voltage SPD Series per U.L. 1449 3rd edition recognition. As long as there is an OCPD anywhere in the system ahead of where Bussmann BSP UL or Low Voltage SPDs is installed it is acceptable. If there is a main, feeder, or branch OCPD feeding a piece of equipment with a Cooper Bussmann BSP UL and Low Voltage family of SPDs in it then the SPDs may be used without any other OCPD protecting the SPD itself.

 

[LMAO]

I got a response from Bussman the other day and neglected to post it.

Logically, you would not use a OCPD on a SPD because it negates the purpose of using SPD; you'd want the SPD to get shorted and protect the load.
But in reality, an unprotected SPD can blow up; it was happening to us at my old job; our SPDs on our VFDs in Africa and everywhere else were exploding because they could not hadle that much current. We were forced to add fuses before the SPD.

 

[petersonra]

Logically, you would not use a OCPD on a SPD because it negates the purpose of using SPD; you'd want the SPD to get shorted and protect the load.
But in reality, an unprotected SPD can blow up; it was happening to us at my old job; our SPDs on our VFDs in Africa and everywhere else were exploding because they could not hadle that much current. We were forced to add fuses before the SPD.

my suspicion is that if you are literally having spds explode, you have a serious power problem that needs fixing, or they were completely misapplied.

 

[ron]

Logically, you would not use a OCPD on a SPD because it negates the purpose of using SPD; you'd want the SPD to get shorted and protect the load.
But in reality, an unprotected SPD can blow up; it was happening to us at my old job; our SPDs on our VFDs in Africa and everywhere else were exploding because they could not handle that much current. We were forced to add fuses before the SPD.

SPD's have short circuit ratings and need to be applied appropriately.

The only SPD's that I've seen fail catastrophically were due to a sustained over voltage, which is why the UL standards was updated to require protection for that.

 

[petersonra]

SPD's have short circuit ratings and need to be applied appropriately.

The only SPD's that I've seen fail catastrophically were due to a sustained over voltage, which is why the UL standards was updated to require protection for that.

actually spds don't need short circuit ratings at present but they are purportedly coming soon.

 

[Jraef]

actually spds don't need short circuit ratings at present but they are purportedly coming soon.

We use fuses ahead of SPDs, but we use Blown Fuse Indicators too so that at least you know.

 

[ron]

actually spds don't need short circuit ratings at present but they are purportedly coming soon.

NEC 2008 Section 285.6

 

[petersonra]

NEC 2008 Section 285.6

Sooner then I thought.

 

[LMAO]

SPD's have short circuit ratings and need to be applied appropriately.

The only SPD's that I've seen fail catastrophically were due to a sustained over voltage, which is why the UL standards was updated to require protection for that.

SPDs have no short circuit ratings; they are placed in "parallel" with the load and source and have no effect on overall short circuit rating of the system.

 

[LMAO]

NEC 2008 Section 285.6

touch?. I was using SPDs in my old job (2011) and I am 99% sure they did not have any short circuit rating.:?

 

[kwired]

actually spds don't need short circuit ratings at present but they are purportedly coming soon.

SPDs have no short circuit ratings; they are placed in "parallel" with the load and source and have no effect on overall short circuit rating of the system.

I am with you LMAO, could someone please explain why they would need a short circuit rating? This type of device is more like a load than switching device. The amount of current that flows when it is shunting a transient is going to depend on conditions of the transient. If there is too much energy behind the transient the device will experience failures - but so would whatever is being protected in same circumstances.

I guess it could be rated on how much current it can safely handle when it fails - but this still seems pointless as the amount of current flowing during a transient is not as predictable as having a fixed supply and knowing what it can deliver.

If normal circuit current enters an assembly containing an SPD and then passes on to the load then we have potential SSC from a load passing through but this is more of a rating for terminals in an enclosure containing the SPD than for the SPD component itself.

 

[T.M.Haja Sahib]

I guess it could be rated on how much current it can safely handle when it fails - but this still seems pointless as the amount of current flowing during a transient is not as predictable as having a fixed supply and knowing what it can deliver.

But there are different classes of SPD's: Some for use at service entrance; some for use at devices inside a home. Their one distinguishing feature is the amount of transient current, they can handle safely: near service entrance they need to handle higher transient current and inside the home, lower handling capacity for transients. Even though transients are unpredictable, their range in a given locality may be more or less predictable and SPD's may be provided accordingly.

 

[ron]

I am with you LMAO, could someone please explain why they would need a short circuit rating? This type of device is more like a load than switching device. The amount of current that flows when it is shunting a transient is going to depend on conditions of the transient. If there is too much energy behind the transient the device will experience failures - but so would whatever is being protected in same circumstances.

I guess it could be rated on how much current it can safely handle when it fails - but this still seems pointless as the amount of current flowing during a transient is not as predictable as having a fixed supply and knowing what it can deliver.

If normal circuit current enters an assembly containing an SPD and then passes on to the load then we have potential SSC from a load passing through but this is more of a rating for terminals in an enclosure containing the SPD than for the SPD component itself.

If there was a fault in the SPD, maybe an MOV that fails short instead of open, how much current can the SPD safely handle without catastrophically failing. That is why a SCR is needed. If there is 200kA available on a SWGR for example, the SPD needs to be rated for 200kA in case that amount of current flows through during a fault in the SPD and we don't want it to blow up, just withstand the fault adequately.

 

[mike_kilroy]

We use fuses ahead of SPDs, but we use Blown Fuse Indicators too so that at least you know.

we package & sell a ditekcorp.com cm series in a small enclosure with 30 amp fuse for overcurrent protect for machine tool protection; they have small led for each phase to show if fuse pops. these are type 2 devices so code regarding fusing and disconnects are section 230.82, 280, and 285 we think. 230.82 if added to supply side of main disconnect. @ 75,000amp TVSS rating we dont expect any to ever fail. some machines that often had drive failures that seemed to be from input high voltage spikes have not had any since installation of these.

 

[T.M.Haja Sahib]

If there was a fault in the SPD, maybe an MOV that fails short instead of open, how much current can the SPD safely handle without catastrophically failing. That is why a SCR is needed. If there is 200kA available on a SWGR for example, the SPD needs to be rated for 200kA in case that amount of current flows through during a fault in the SPD and we don't want it to blow up, just withstand the fault adequately.

After successfully interrupting the transient current through it, the SPD offers a very high impedance to the power frequency follow on current so that power frequency leakage current is negligible. But if the SPD fails, a short circuit could develop and a suitable protective device upstream to the SPD is necessary in this case.
A SPD is rated for transient current and not for power frequency short circuit current.