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Short circuit through ground
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Karl Fischer
- User
- Posts: 3
- Joined: Wed Jun 07, 2017 7:42 pm
Short circuit through ground
I want to use a variac with a rectifier bridge and capacitor as a variable DC source. Because a variac is not shielded from the mains I see a possible problem. Is it safe to connect my 2205A (x100 probe) to this source or do I risk creating a short circuit through the ground via the PC?
Re: Short circuit through ground
Hi Karl,
With any measurement of potentially hazardous voltages (as you would have, using a Variac on mains voltage) you should only be considering tools appropriate for the job.
The correct Probe to use would be a 1000V (minimum) CAT III Differential Probe, not a x100 Probe (which would mean you would be shorting one of the connections to ground) and not even 2 x100 Probes (which would mean avoiding the short to ground, but would still mean that in the event of any error or failure YOU may well be the shortest route to ground for a dangerous current). Differential Probes can be quite a bit more expensive (especially if they are Active Differential Probes), but then protection from these hazards, while maintaining reasonable accuracy/precision, and bandwidth doesn't come cheap.
We have a Range of Active Differential Probes here: https://www.picotech.com/accessories/ac ... ope-probes.
Regards,
Gerry
With any measurement of potentially hazardous voltages (as you would have, using a Variac on mains voltage) you should only be considering tools appropriate for the job.
The correct Probe to use would be a 1000V (minimum) CAT III Differential Probe, not a x100 Probe (which would mean you would be shorting one of the connections to ground) and not even 2 x100 Probes (which would mean avoiding the short to ground, but would still mean that in the event of any error or failure YOU may well be the shortest route to ground for a dangerous current). Differential Probes can be quite a bit more expensive (especially if they are Active Differential Probes), but then protection from these hazards, while maintaining reasonable accuracy/precision, and bandwidth doesn't come cheap.
We have a Range of Active Differential Probes here: https://www.picotech.com/accessories/ac ... ope-probes.
Regards,
Gerry
Gerry
Technical Specialist
Technical Specialist
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Karl Fischer
- User
- Posts: 3
- Joined: Wed Jun 07, 2017 7:42 pm
Re: Short circuit through ground
Thanks Gerry,
The variac is off the table. For the DC power supply I will stick to series of 12 volt batteries. A little less variable but no connection to the mains.
The variac is off the table. For the DC power supply I will stick to series of 12 volt batteries. A little less variable but no connection to the mains.
Re: Short circuit through ground
Hi karl,
That sounds like a safer, easier option.
Just to prevent any possible misunderstanding regarding my previous statement (for other visitors to this forum) a 700V DC + peak AC probe such as our TA041 Differential Probe, would be sufficient to cover 230V RMS. You also need to cover the impulse energy of possible transients, and our TA041 Probe is rated at 1000V CAT III, which covers +/-1400V DC + peak AC as an absolute maximum voltage. However, if you were not selecting a probe from our range then you could also look for a CAT II probe but it would also have to be 1000V (the next lowest CAT voltage rating would be 600V which is not enough for 230V RMS, and is why I said '1000V minimum').
Regards,
Gerry
That sounds like a safer, easier option.
Just to prevent any possible misunderstanding regarding my previous statement (for other visitors to this forum) a 700V DC + peak AC probe such as our TA041 Differential Probe, would be sufficient to cover 230V RMS. You also need to cover the impulse energy of possible transients, and our TA041 Probe is rated at 1000V CAT III, which covers +/-1400V DC + peak AC as an absolute maximum voltage. However, if you were not selecting a probe from our range then you could also look for a CAT II probe but it would also have to be 1000V (the next lowest CAT voltage rating would be 600V which is not enough for 230V RMS, and is why I said '1000V minimum').
Regards,
Gerry
Gerry
Technical Specialist
Technical Specialist