Electrical Surge Protection Devices

[david96]

Surge Protection Devices (SPDs) Informative only.

Guidance on the installation of SPDs to provide limitation of transient overvoltages caused by powerline disturbances and by natural events, such as lightning strikes to, or near to exposed conductors.

AS/NZ 1768 provides for a detailed risk assessment on the need for lightning and surge protection.

The risk assessment for normal domestic installations with regard to lightning protection is generally

very low. However one or more of the following conditions could warrant the installation of SPDs.

1 Where lightning is prevalent.

2 Where power disturbances are frequent eg industrial areas.

3 Where the site is located at the end of long overhead power lines.

4 Where the site is exposed eg, on a hill.

5 Where houses may be several hundreds or more metres apart eg in rural areas.

6 Where the installation contains electronic equipment eg, computers or computer network.

Location Primary SPDs should be installed near the origin of the electrical installation or in the main switchboard.

Where the premises contain sensitive electronic equipment secondary protection in the form of plug in surge filters may be warranted.

Installation

After the main switch but prior to any RCD device.

With the MEN system between the phase and the neutral bar or earth bar.

With a TT system two SPDs may be required one from phase to earth and one from neutral to earth.

Surge rating should be 40kA for an 8/20 microsecond impulse and a minimum voltage of 275V ac.

In the case of some installations in exposed locations SPDs with higher surge rating eg, 100kA.

SPDs should be protected from short circuit by an MCB or HRC fuse rated at not less than 32A in the case of a 40kA device or other means as recomended by the manufacturer. Connection conductor between phase and SPD and SPD to neutral or earth bar should be as short as practicable 300mm to 600mm overall. Minimum size 6sq mm.

[Crossy]

David. Do you have any part numbers and sources for suitable devices that are (reasonably) readily available in Thailand?

There's another thread somewhere discussing MOVs and their use here.

[Tywais]

For those interested in more details of surge protection:

How Surge Protectors Work

more technical side:

AC line voltage suppression .pdf

Principles .pdf

I'm looking at the different techniques now for an application at the lab. I am installing some electronics into a HV top terminal (225kV relative to earth ground) in an ION implanter and will be using a combination of MOVs and TVS to protect from possible HV gradients in the system. Tricky process.

[Cuban]

From one of the sites mentioned above:

One problem with surge protectors is that the MOVs can burn out with one good surge. This is why it's good to get a protector with an indicator light that tells you whether or not it's functioning properly.

The issue about telephone lines and fast protection of the equipment connected to it interests me.

Apart from DIY solutions * similar to diagrams in the web site mentioned in the above post, I have not seen anything on sale in Thailand.

* Low value fuses in each leg and a more attracive path to earth.

[david96]

David. Do you have any part numbers and sources for suitable devices that are (reasonably) readily available in Thailand?

There's another thread somewhere discussing MOVs and their use here.

They are available in DIN rail mounting. They are readily available in Australia and are now becoming more widely used.

In Thailand it might be advisable to contact a major electrical equipment importer. Eg For HPM/Clipsal/ Schneider/ AAB etc.

The DIN rail types have an indicating device green OK, red replace plug-in module. Some can be fitted with aux. contacts for remote indication if required.

For tech info on SPDs and installation refer to this website (Clipsal)

http://www.clipsal.com/trade/__data/page/81/I39.pdf

Edited June 14, 2008 by david96

[petercsea]

David. Do you have any part numbers and sources for suitable devices that are (reasonably) readily available in Thailand?

There's another thread somewhere discussing MOVs and their use here.

They are available in DIN rail mounting. They are readily available in Australia and are now becoming more widely used.

In Thailand it might be advisable to contact a major electrical equipment importer. Eg For HPM/Clipsal/ Schneider/ AAB etc.

The DIN rail types have an indicating device green OK, red replace plug-in module. Some can be fitted with aux. contacts for remote indication if required.

For tech info on SPDs and installation refer to this website (Clipsal)

http://www.clipsal.com/trade/__data/page/81/I39.pdf

see: www.schneider-electric.co.th/surge/

Easily available for approx 2000 baht. 100,000 Baht guarantee offered.