Why a breaker size limit, on a whole panel/whole house surge protector?

Status
Not open for further replies.
B

brycenesbitt

Senior Member
Location
United States
I'm reading through the install sheet for an Intermatic IG1200RC3 and there's something confusing. The section under a Type 2 install reads:

For best performance from SPD the maximum recommended circuit breaker size of 240V, 20A, 2-pole should be used.

Why would the breaker size matter? If the breaker were ever to trip, the device would be disconnected from the panel and offer no protection. If the breaker does not trip, the device should receive full current as if there was no breaker at all. (I'm intending to use a spare breaker in the bottom right position, to protect various compressors, pumps and electrical equipment on the other breakers).
 
Last edited:
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
My guess is that you almost have the answer.
When a surge event occurs the SPD will be drawing a high current as it absorbs surge energy.
You do not want the magnetic trip of the breaker to respond to that surge by opening if you can safely prevent that.
So, you want to use the largest breaker that will still protect the SPD.

Tapatalk!
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
ptonsparky said:
I can make you something that will call, text, email, or initiate either/both audible/visible alerts upon failure if desired. Special, today only, for $9999. Call within the next 5 minutes and you will get not one but....:)
Click to expand...

will there be separate shipping and handling charges on the 2nd unit ? :D
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
The only time the breaker will trip is when the SPD has had a catastrophic failure. If the SPD fails then it isn't offering protection anyway.

The breaker will not respond to the high surge current. If breakers acted this fast then all SPDs would not be needed.

SPDs will eventually fail and stop protecting the circuit. Protective equipment can not just be installed and ignored. Routine/regular maintenance is mandatory, even if the time line is measured in years.
 
Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
GoldDigger said:
My guess is that you almost have the answer.
When a surge event occurs the SPD will be drawing a high current as it absorbs surge energy.
You do not want the magnetic trip of the breaker to respond to that surge by opening if you can safely prevent that.
So, you want to use the largest breaker that will still protect the SPD.

Tapatalk!
Click to expand...

When the surge hits, doesn't the SPD get damaged anyways? Basically it sacrifices its life (up to the rating) to protect the interior equipment. So, why not install a larger breaker and larger gauge wire? The SPD it self does not draw very much current any way.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
edward said:
When the surge hits, doesn't the SPD get damaged anyways? Basically it sacrifices its life (up to the rating) to protect the interior equipment. So, why not install a larger breaker and larger gauge wire? The SPD it self does not draw very much current any way.
Click to expand...

Most SPDs are able to handle many surges over their life, they are not usually intended to be 'once and done'.

In some cases the wire size may have been included in the performance of the device. Changing the wire size and length may have adverse affects on the device's performance.

For all intents, SPDs do not draw any current.
 
Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
jim dungar said:
Most SPDs are able to handle many surges over their life, they are not usually intended to be 'once and done'.

In some cases the wire size may have been included in the performance of the device. Changing the wire size and length may have adverse affects on the device's performance. That makes sense
Click to expand...

One of SQUARE-D unit that is field wired, only has 30A limitation, But why limited to 30 amps? Why does it not make sense to go larger?
 
Ponchik

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
edward said:
One of SQUARE-D unit that is field wired, only has 30A limitation, But why limited to 30 amps? Why does it not make sense to go larger?
Click to expand...

I called the SQUARE-D TVSS technical department and the engineer said:

"Most of the residential SPD are limited to 12AWG and 20A max OCPD and the commercial SPD are limited to 10AWG and 30A max OCPD. Because since the transient voltage is only for nano second it does not make sense to go any higher than the 12 awg & 10 awg with respected OCPD. Besides the SPD it self does not draw any current it self anyway, so going with larger gauge conductor is waste of material without any gain"
 
B

broadgage

Senior Member
Location
London, England
Under normal operating conditions it would not matter if a surge protective device was connected via a larger breaker than specified, though so doing would be a violation.

If however the surge protective device suffered an internal short circuit, then a larger OCPD will result in more damage and more risk of fire, the device itself is already a write off, the concern would be explosive rather than passive failure with risk of burning fragments being ejected.
 
B

brycenesbitt

Senior Member
Location
United States
Ok, got it. Based on the above:

Since this model SPD device is fed by 12 gauge wire, the maximum breaker size by code is 20 amps. Simple.
Since an SPD may draw a lot of current, the minimum recommended size is 20 amps. Got it.
Typical thermal-magnetic breakers tend to pass high current transients without tripping. Good to know.

This link was particularly helpful, thanks: http://ecmweb.com/power-quality/basi...rge-protectors

---------------------------
Since my particular device is a dual rated Type 1/Type 2 it may be installed on either side of the breaker. The device in fact appears oddly robust: perhaps to contain the melted metal that a catastrophic failure might bring if, for example, the Type 1 installed device went to permanent dead short L1-N or L2-N. If the device suddenly drew 100 amps continuous the incoming leads would melt.

---------------------------
Also to summarize:
A dedicated breaker will never be deactivated by an unrelated fault, and allows easy testing and isolation of the SPD.
A shared breaker with a critical service (like a lighting load) will be self-checking. If the breaker is tripped, chances are a building occupant will notice and complain.

The level of protection is the same between the options. The level of protection has more to do with the length of wire to the SPD and the sharpness of any bends taken by the wiring (less sharp is better). The inductance of the wire itself is the limiting factor on the response time of the SPD to a transient. Snake oil is used liberally in SPD specification sheets and true performance is difficult to measure or compare.

-----------------------------
And to add to the discussion.
Installing the SPD behind an AFCI/GFCI or CAFCI is a bad idea. Those devices could trip under the exact conditions that merit the need for the SPD to be active. An SPD however can protect other fancy electronic breakers in the same panel, which could be a significant savings given the cost of replacing a whole panel full of AFCI's.

So bottom line: either use a Type 1 and ignore the breaker issue, or use a Type 2 behind a regular or high inrush breaker of the maximum size supported by your SPD.
 
Last edited:
B

brycenesbitt

Senior Member
Location
United States
Status
Not open for further replies.
Top