whole house SPD
- Thread starter mannyb
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
To protect from outside surges, at the service; from internal surges, closest to the protected equipment.
The best protection is cascaded; hard-wired at service and plug-in or hard-wired nearest point of use.
No to shared lugs unless listed for multiple wires. Most use a dedicated breaker for hard-wired devices.
The best protection is cascaded; hard-wired at service and plug-in or hard-wired nearest point of use.
No to shared lugs unless listed for multiple wires. Most use a dedicated breaker for hard-wired devices.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
230.67(B) Exception allows connection at the first downstream panel. But as Larry indicated, you are going to need to connect it thru a breaker due to lug listing issues even it it is a Type 1.
Greentagger
Senior Member
- Location
- Texas
- Occupation
- Master Electrician, Electrical Inspector
Been thinking about the lug issue too for a type 1SPD. Wonder if those insulated piercing tap connector s would work and be compliant?
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
230.67 has an exception, the SPD can be located at each next level distribution downstream and is required to be type 1 or type 2. Downstream you would use a type 2
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
This is the conventional wisdom. I don't know how true it is. It makes sense but I don't know if there is any actual science to support the idea that one gets any substantial extra protection from multiple layers of SPD. Most electronics these days has already been hardened against surges already. Not sure what you gain by adding another layer.
There is a lot of confusion because a SPD is not like a breaker or fuse. Most are metal oxide varistors. This is a voltage variable resistor that is nearly open circuit at normal line voltage and becomes a low resistance at higher voltages. It is in parallel to the loads, NOT series. So you have to look at the surge impedance to calculate the voltage seen by a load. In residential wiring it’s about 20 V per inch plus you have to add the MCOV (voltage rating) of the MOV. Most standards for equipment require 200% of line voltage plus 1,000 V so 300 V NM is good to 1600 V but typically arcs around 3-4 kV so we need not worry about anything higher. That’s why the 100+ kV BIL claims of SPDs are ridiculous. Motors are only required to meet a minimum surge of 1000 V. So using that as a cutoff with a 300 V MOV and figuring 20 V per inch gives us 35 inches away based on (1000 V - 300 V / 20 V/inch. So a “whole house” SPD is really strictly a main panel SPD. It does help bring down the peak and works in conjunction with downstream SPDs to absorb say s lightning strike but it in no way offers significant protection to devices anywhere outside the main panel. SPD requirements were added to
NEC strictly to protect electronics in AFCIs in the main panel. It won’t do anything for expensive electronics.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Also, read the fine print in protected-equipment warranties.
kwired
Electron manager
- Location
- NE Nebraska
Yes. whole house warranty is only good if you have additional protection at the equipment.
Equipment devices only have warranty if there is a whole house device back at service or a main panel.
They know that the one at the panel will usually significantly knock the surge level coming in from supply side down and the equipment device will catch whatever still makes it to the equipment level of premises wiring
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