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SDP for a DB feeding external loads

Apostolos

Good morning

I think this question, or similar ones, may come back again and again.

We have a building with Faraday cage lightning protection

So in the Main Distribution Panel we have included a T1+2 surge protection

Couple of floors up, we have a mechanical DB feeding condenser units that are exposed in the roof.

We also have an external services DB that is feeding external lighting (columns, bollards etc)

Now, I know that usually the sub DBs are being protected by T2 only SPD.

However I am reading that T1 is about direct lightning strike and I am wondering wether for these 2 DBs only I should use a T1+2 assuming that both the condensers on the roof or the lighting columns may be subject to a direct strike

I really would like your opinion on this.

Should I stick to a T2 or go to a T1+2 based on my train of thought above?

Thanks!

Parents

  • Hi,

    First of all, I’d like to point out that the general rule of using Type 2 SPDs for distribution boards and Type 1 for the main panel is not always correct. It’s essential to carry out a proper risk assessment to determine the correct SPD type and location. Risk assesment takes several factors into account and we calculate risk levels. 

    However, with experience, and after considering and eliminating several influencing factors — such as the type of building, location, Area (rural or Urban) earthing arrangement, and presence of an LPS — we often simplify the process. That’s when a practical rule of thumb is applied: typically, Type 2 SPDs are used for distribution and sub-distribution boards, while Type 1 SPDs are installed at the main panel board. 

    However, there is no very straightforward way to decide SPD selection in some cases. (Example: I have never come across any regulation or standard so far that tells you how far a DB needs to be from LPS conductors / earthing conductors or other DBs to go ahead with a T2 SPD ). This is normally, a Highly Site Specific Process. 

    So, Once you have a good understanding, the decision is yours to make, given you have a in depth knowledge. 

    in your case, I would say it's safe to go with T1+2 SPD if you are not in a position to do a comprehensive Risk Assessment.  I know it's not the cost effective solution. But its not worth the risk. 


Reply

  • Hi,

    First of all, I’d like to point out that the general rule of using Type 2 SPDs for distribution boards and Type 1 for the main panel is not always correct. It’s essential to carry out a proper risk assessment to determine the correct SPD type and location. Risk assesment takes several factors into account and we calculate risk levels. 

    However, with experience, and after considering and eliminating several influencing factors — such as the type of building, location, Area (rural or Urban) earthing arrangement, and presence of an LPS — we often simplify the process. That’s when a practical rule of thumb is applied: typically, Type 2 SPDs are used for distribution and sub-distribution boards, while Type 1 SPDs are installed at the main panel board. 

    However, there is no very straightforward way to decide SPD selection in some cases. (Example: I have never come across any regulation or standard so far that tells you how far a DB needs to be from LPS conductors / earthing conductors or other DBs to go ahead with a T2 SPD ). This is normally, a Highly Site Specific Process. 

    So, Once you have a good understanding, the decision is yours to make, given you have a in depth knowledge. 

    in your case, I would say it's safe to go with T1+2 SPD if you are not in a position to do a comprehensive Risk Assessment.  I know it's not the cost effective solution. But its not worth the risk. 


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