SPD Requirement at Distribuition Board Level(Branch circuit panel)

[Sajid khan]

Our Electrical consultant has designed Type-1 (or 1+2) SPDs on the main Low voltage distribution panel (Transformer secondary), Type-2 at Sub-Main distribution panel and Type-3 at end circuit distribution boards. Can you guide on following queries:
1. If SPDs are provided upstream (say, Main LV panel and Sub main panel), do we still need the type-3 SPD at end circuit Distribution board?
2. Please assume there is no calculated risk assessment done, however due the nature of the building (Hospital) assume critical / expensive equipment that might be plugged in
3. The building is located in Lightning Protection Level I (LPL-I)

Regards


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[drktmplr12]

Our Electrical consultant has designed Type-1 (or 1+2) SPDs on the main Low voltage distribution panel (Transformer secondary), Type-2 at Sub-Main distribution panel and Type-3 at end circuit distribution boards. Can you guide on following queries:
1. If SPDs are provided upstream (say, Main LV panel and Sub main panel), do we still need the type-3 SPD at end circuit Distribution board?
2. Please assume there is no calculated risk assessment done, however due the nature of the building (Hospital) assume critical / expensive equipment that might be plugged in
3. The building is located in Lightning Protection Level I (LPL-I)

Regards


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Usually, the most damaging surges come in through the utility service and a direct strike of nearby, unprotected equipment. Nearby strikes can also induce damaging surges downstream of the main distribution gear, regardless if the building is protected LPL-1, and so a type 1 SPD on a switchboard may not necessarily clamp enough to protect a 120-volt device one, two or three panels downstream, for example. think of it like stages of protection. each of the three types limits transient voltages further and further.

An SPD is cheap insurance if critical/expensive equipment is involved. ask yourself another question, what is the tradeoff in eliminating the Type 3?

 

[petersonra]

Our Electrical consultant has designed Type-1 (or 1+2) SPDs on the main Low voltage distribution panel (Transformer secondary), Type-2 at Sub-Main distribution panel and Type-3 at end circuit distribution boards. Can you guide on following queries:
1. If SPDs are provided upstream (say, Main LV panel and Sub main panel), do we still need the type-3 SPD at end circuit Distribution board?
2. Please assume there is no calculated risk assessment done, however due the nature of the building (Hospital) assume critical / expensive equipment that might be plugged in
3. The building is located in Lightning Protection Level I (LPL-I)

Regards


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The clamping voltage is different for the different Types of SPDs. The closer it is to the service the higher the clamping voltage.

My personal opinion is that the SPD closest to the device being protected will do the most good because the clamping voltage is lowest.

OTOH, most modern electrical and electronic devices are inherently resistant to surges. So, maybe SPDs are no longer all that important.

 

[Sajid khan]

Usually, the most damaging surges come in through the utility service and a direct strike of nearby, unprotected equipment. Nearby strikes can also induce damaging surges downstream of the main distribution gear, regardless if the building is protected LPL-1, and so a type 1 SPD on a switchboard may not necessarily clamp enough to protect a 120-volt device one, two or three panels downstream, for example. think of it like stages of protection. each of the three types limits transient voltages further and further.

An SPD is cheap insurance if critical/expensive equipment is involved. ask yourself another question, what is the tradeoff in eliminating the Type 3?

Yes agreed, some time we have sensitive electronic power supplies and Lighting switch actuators etc in the Panel board at branch distribution level which may damage in the absence of level-3 SPD.
And, the SPD is most critical in application where Panel boards are feeding the sensitive medical equipment for instance imaging equipment although the medical equipment most probably have the SPD but you never know or should not relie on the medical equipment manufacturer as it varies by manufacturer.


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[jrohe]

Our Electrical consultant has designed Type-1 (or 1+2) SPDs on the main Low voltage distribution panel (Transformer secondary), Type-2 at Sub-Main distribution panel and Type-3 at end circuit distribution boards. Can you guide on following queries:
1. If SPDs are provided upstream (say, Main LV panel and Sub main panel), do we still need the type-3 SPD at end circuit Distribution board?
2. Please assume there is no calculated risk assessment done, however due the nature of the building (Hospital) assume critical / expensive equipment that might be plugged in
3. The building is located in Lightning Protection Level I (LPL-I)

Regards


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NEC section 517.26 requires compliance with Article 700 unless modified within Article 517. NEC section 700.8 requires a listed SPD to be installed at all emergency system switchboards and panelboards.

 

[drktmplr12]

NEC section 517.26 requires compliance with Article 700 unless modified within Article 517. NEC section 700.8 requires a listed SPD to be installed at all emergency system switchboards and panelboards.

i would take exception to the "emergency system" and instead clarify as "life safety branches". I would expect not all load panels with emergency power are considered life safety, but all life safety panels are backed up by emergency power.

 

[jrohe]

i would take exception to the "emergency system" and instead clarify as "life safety branches". I would expect not all load panels with emergency power are considered life safety, but all life safety panels are backed up by emergency power.

I understand where you're going with this. I, also, do not like the use of the term "emergency" as a blanket term for any system that is backed up by a generator or other standby power source. However, the title of Article 700, which I referenced above is "Emergency Systems" so it was appropriately used in context.

I acknowledge there are several types of standby power systems, including the Article 517 "essential electrical system," which is comprised of the life safety, critical, and equipment branches, Article 700 emergency systems, Article 701 legally required standby systems, and Article 702 optional standby systems. Instead of the typical "emergency generator" blanket term, it would be much more appropriate to call them "standby generators" unless the generator was dedicated exclusively to a health care facility's life safety branch or dedicated exclusively to an Article 700 system.