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## 21-06-2015

### Versão atual de: PhDfromthewest , 21-06-2015

#### Texto:

 Derived from my reply to a post above: Something to remember, but an AC utility ground is NOT always ground. I work with high power systems and there is always a lot to consider. Assuming your building electrical is correctly wired per NEC, there is still significant inductance to the point at the main panel where the ground rod or ufer (e.g., the building rebar system) grounds the electrical system. NEC requires main building ground at a single point which is at the service entrance panel (NOT a branch panel). So when you get a severe fault to ground and a large change in current (recall: V=L*dI/dt), you can get a huge potential difference that can kill along the fault current ground path. If your are next to the fault, not much of a problem. But if you are away from the fault and unfortunately along the path of the fault current, there can be a very large voltage on the ground. I have seen grounded metal panels arc against frames that they were "attached" to... Assuming your building electrical is correctly wired per NEC, there is still significant inductance to the point at the main panel where the ground rod or ufer (e.g., the building rebar system) grounds the electrical system. NEC requires main building ground at a single point which is at the service entrance panel (NOT a branch panel). So when you get a severe fault to ground and a large change in current (recall: V=L*dI/dt), you can get a huge potential difference that can kill along the fault current ground path. If your are next to the fault, not much of a problem. But if you are away from the fault and unfortunately along the path of the fault current, there can be a very large voltage on the ground. I have seen grounded metal panels arc against frames that they were "attached" to... An alternative is to run your own dedicated ground to the main panel and stay off the AC grounds. If that is a long way away and you are on a ground floor, get the floor surveyed and pop a hole in the floor. Buy an NEC ground rod (6' long) and drive into the ground leaving a few inches exposed to tie your ESD mat to. A tie in to an UNCOATED WATER pipe (most modern installations are plastic sleeved and therefore dicey as they are insulating!!!) that is embedded and stubs out from the concrete or a true ufer is also a good idea. Again, per NEC, that pipe should be tied to the AC electrical ground, but your are protected from AC fault currents by the low resistance of the concrete along the length IF it is not sleeved.

`open`

## 21-06-2015

### Editado por: PhDfromthewest , 21-06-2015

#### Texto:

 Derived from my reply to a post above: Something to remember, but an AC utility ground is NOT always ground. I work with high power systems and there is always a lot to consider. Assuming your building electrical is correctly wired per NEC, there is still significant inductance to the point at the main panel where the ground rod or ufer (e.g., the building rebar system) grounds the electrical system. NEC requires "singlemain building ground at a single point grounds."which is the service entrance panel (NOT a branch panel). So when you get a severe fault to ground and a large change in current (recall: V=L*dI/dt), you can get a huge potential difference that can kill along the fault current ground path. If your are next to the fault, not much of a problem. But if you are away from the fault and unfortunately along the path of the fault current, there can be a very large voltage on the ground. I have seen grounded metal panels arc against frames that they were "attached" to... Assuming your building electrical is correctly wired per NEC, there is still significant inductance to the point at the main panel where the ground rod or ufer (e.g., the building rebar system) grounds the electrical system. NEC requires "singlemain building ground at a single point grounds."which is the service entrance panel (NOT a branch panel). So when you get a severe fault to ground and a large change in current (recall: V=L*dI/dt), you can get a huge potential difference that can kill along the fault current ground path. If your are next to the fault, not much of a problem. But if you are away from the fault and unfortunately along the path of the fault current, there can be a very large voltage on the ground. I have seen grounded metal panels arc against frames that they were "attached" to... An alternative is to run your own dedicated ground to the main panel and stay off the AC grounds. If that is a long way away and you are on a ground floor, get the floor surveyed and pop a hole in the floor. Buy an NEC ground rod (6' long) and drive into the ground leaving a few inches exposed to tie your ESD mat to. A tie in to an UNCOATED WATER pipe (most modern installations are plastic sleeved and therefore dicey as they are insulating!!!) that is embedded and stubs out from the concrete or a true ufer is also a good idea. Again, per NEC, that pipe should be tied to the AC electrical ground, but your are protected from AC fault currents by the low resistance of the concrete along the length IF it is not sleeved.

`open`

## 21-06-2015

### Postagem original de: PhDfromthewest , 21-06-2015

#### Texto:

```Derived from my reply to a post above:

Something to remember, but an AC utility ground is NOT always ground. I work with high power systems and there is always a lot to consider.

Assuming your building electrical is correctly wired per NEC, there is still significant inductance to the point at the main panel where the ground rod or ufer (e.g., the building rebar system) grounds the electrical system. NEC requires "single point grounds." So when you get a severe fault to ground and a large change in current (recall: V=L*dI/dt), you can get a huge potential difference that can kill along the fault current ground path. If your are next to the fault, not much of a problem. But if you are away from the fault and unfortunately along the path of the fault current, there can be a very large voltage on the ground. I have seen grounded metal panels arc against frames that they were "attached" to...

An alternative is to run your own dedicated ground to the main panel and stay off the AC grounds. If that is a long way away and you are on a ground floor, get the floor surveyed and pop a hole in the floor. Buy an NEC ground rod (6' long) and drive into the ground leaving a few inches exposed to tie your ESD mat to. A tie in to an UNCOATED WATER pipe (most modern installations are plastic sleeved and therefore dicey as they are insulating!!!) that is embedded and stubs out from the concrete or a true ufer is also a good idea. Again, per NEC, that pipe should be tied to the AC electrical ground, but your are protected from AC fault currents by the low resistance of the concrete along the length IF it is not sleeved.```

`open`