Surge Protection

[danmoriarty]

Hi guys

I have a read through Reg. 534 and i need someone to help me understand it.I am trying to make a decision on what device(s) to use and i need a little bit of clarification. I have initially thought to utilise cascading and use two devices: Hager SPN215R and SPN208S. The reason for this i that i have (as some may have seen me discuss before) my main board and another board which houses network equipment etc.

I dont believe the house to be extremely vulnerable to lightning but it is farely high up on a mountain side with no near by buildings.now I know the SPN215R is ok for the general protection of the house, but would this protect the network equipment? or am i right in assuming that i will also require both devices, one for general protection and one for fine protection? or would i just need SPN208S, does that cover both? I dont need to go as far as a class three do i?

Its a TT system, single phase 80A supply

Heres a link for reference: http://www.hager.co.uk/products/energy-distribution/protection-devices/surge-protection-devices/8028.htm

Thanks in advance

 

[SLIPSHOD & SLAPDASH]

Do these devices Really work ? I notice the Hagar ones have a replaceable cartridge, is this a capacitor ?

 

[Marvo]

Not a capacitor, a semiconductor with a clamping voltage which if it's exceeded the device conducts to ground (earth) to prevent the high voltages reaching the sensitive equipment. There's no limiter on these devices as such so sometimes the semiconductor material survives the surge, sometimes so much current flows that it burns out. They often have some kind of indication when they've been destroyed so you can replace the cartridge or even the entire device.

Edit; Yes, they do work, they're not a gimmick. Like I say they do have limitations so if there's a very close lightning strike or a massive surge they might not be able to sink all the high voltages before they blow.

 

[SLIPSHOD & SLAPDASH]

Ok, so say a house is hit by lightning or has a huge surge & this unit does its job and connects to earth. How is any cable (which may be a 4mm on a TT system) carry that to earth ?

 

[Marvo]

I would consider a 4mm earth wire very small especially for a system that's not pme. A wire 4mmsq will take around 1200Amps for 1 second before going molten so it would be fairly capable of sinking high voltage transients which generally last for milliseconds.

 

[danmoriarty]

While we're at it. Lets assume my house is hit by lightning. How do you know where that current is heading? Is it not more likely to travel "backwards" through an installation, from let's say the highest lamp you have in your house and follow that path to board and out?

Is this type of device just protecting you from in coming line surges?

Hoping to get some knowledge laid on me

 

[SLIPSHOD & SLAPDASH]

I do not believe anything like this can protect sensitive electronics from a lightning strike. I have been told running all through a UPS can help a lot ?

 

[Marvo]

I'm not sure surge arrestors would protect anything if there was a direct lightning strike on an installation, I was talking about a strike in the local area with high voltages on the incoming supply. The only protection I know of for a direct strike is lightning rods which also provide an easy direct path to ground but they're.not really connected to the electrical installation of a premises the same way surge arrestors are.

A ups should protect against supply high voltages/surges but again I think it would offer only limited protection at best against a direct strike.

I think the discussions of the effects of a direct strike might be better as a separate topic as surge arrestors aren't designed to protect against them.

To be honest I know a little about transient high voltages on LV networks and consumer protection but I don't know much about the effects of a direct strike on an installation.

 

[steptoe]

I think if my house has a direct strike my TV still working will be way down my list of worries.! :|

 

[SLIPSHOD & SLAPDASH]

Is my underpants draw intact may be on the list

 

[Technician]

Not a capacitor, a semiconductor with a clamping voltage which if it's exceeded the device conducts to ground (earth) to prevent the high voltages reaching the sensitive equipment. There's no limiter on these devices as such so sometimes the semiconductor material survives the surge, sometimes so much current flows that it burns out. They often have some kind of indication when they've been destroyed so you can replace the cartridge or even the entire device.

Edit; Yes, they do work, they're not a gimmick. Like I say they do have limitations so if there's a very close lightning strike or a massive surge they might not be able to sink all the high voltages before they blow.

Is this semiconductor behaving something like a Zener barrier,

or is it a little bit more clever than this simple device?

 

[pickleye]

Is my underpants draw intact may be on the list

"Like" button

 

[Marvo]

Is this semiconductor behaving something like a Zener barrier,

or is it a little bit more clever than this simple device?

These devices aren't clever as such. Zener diodes are often used in surge protectors along with varistors. Zeners have a faster response time but generally can't handle the same energy that varistors can. Because of the different characteristics they often mix the two components in the same arrestor to combine good response time with current handling ability.

 

[Tony S]

Look up transorb on Google. That should answer your questions.