Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 5 replies
  • Subscribers 37 subscribers
  • Views 620 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Surge Protective Devices and High Ra.

Zoomup

What adverse effects can be expected under over Voltage fault conditions, when an S.P.D. is required to operate  on a TT system with a high Ra.

Longer duration fault transient Voltages?

Higher fault Voltages supplied to vulnerable equipment?

"3.2.2 Time/energy relationship The current must flow for sufficient time to deposit enough energy within electronic components to cause damage – commonly the melting down of some part of the device. 3.3 Surge protection devices (SPDs) – how they work Surge protection devices (see the glossary – Appendix B for other commonly-used terms for these) limit the transient voltage to a level which is safe for the equipment they protect by conducting the large surge current safely to ground through the earth conductor system. Current flows past, rather than through, the protected equipment and the SPD thereby diverts the surge (see figure 8). The SPD limits both common and difference mode voltages to the equipment."

Z.

Parents
  • 0

    Thinking further today I was looking at Figure 16A3. I was particularly interested in item 3a, the gas discharge tube connected between N and E. I do not know how the operation of the 3a item is affected by the Ra of the system. Say a, Ra is 50 Ohms, or b, 100 Ohms, or c, 500 Ohms or d, 1000 Ohms or e, 1500 Ohms .With a very high transient spike how would the operation of 3a be affected?

    A high Ra will make some difference, but not have much of an effect I would have thought. The device will sense the overvoltage and start conducting as normal - the current flow to Earth may be much reduced but the resulting voltage between the SPDs terminals should be much the same as for a TN system (or if anything perhaps a little lower due to the reduced current). The voltage on both terminals might be a lot higher above true Earth than on a TN system - but the protected devices (downstream) don't see that - they should only be exposed to the voltage difference between the SPD's terminals (L on one end and PE (or N) on the other - which is why we have to keep the connections between the SPD and the point it connects to the circuit it protects short.

       - Andy.

Reply
  • 0

    Thinking further today I was looking at Figure 16A3. I was particularly interested in item 3a, the gas discharge tube connected between N and E. I do not know how the operation of the 3a item is affected by the Ra of the system. Say a, Ra is 50 Ohms, or b, 100 Ohms, or c, 500 Ohms or d, 1000 Ohms or e, 1500 Ohms .With a very high transient spike how would the operation of 3a be affected?

    A high Ra will make some difference, but not have much of an effect I would have thought. The device will sense the overvoltage and start conducting as normal - the current flow to Earth may be much reduced but the resulting voltage between the SPDs terminals should be much the same as for a TN system (or if anything perhaps a little lower due to the reduced current). The voltage on both terminals might be a lot higher above true Earth than on a TN system - but the protected devices (downstream) don't see that - they should only be exposed to the voltage difference between the SPD's terminals (L on one end and PE (or N) on the other - which is why we have to keep the connections between the SPD and the point it connects to the circuit it protects short.

       - Andy.

Children
No Data

Community Rules & Guidelines