[RE-wrenches] Clamping CTs Around Live Conductors - White Paper References and/or Anecdotal Information Requested

[Kent]

Sam,

As long as the CT leads are properly terminated, opening or closing the 
clamp-on CT core is nothing different that what a clamp-on ammeter is 
doing. Make a mistake and pull the leads out of the multimeter and you 
may have a high voltage arc. There are other problems with using a 
multimeter in this manner: 1) that the current ranges are usually fused 
and the fuse may not clear a high voltage arc, and 2) switching current 
ranges may temporarily open the circuit.

Kent Osterberg
Blue Mountain Solar


On 3/8/2024 8:29 AM, Sam Haraldson via RE-wrenches wrote:
> Dear Wrenches,
>
> I'm trying to determine whether or not it is acceptable to clamp 
> monitoring CTs around hot conductors.  For this question please assume 
> the CT wires are landed in their proper terminals and that proper 
> PPE/safety protocol is employed. The monitored currents in question 
> are residential services of 600A or less. Is there harm to the CT by 
> clamping them around a hot conductor?
>
> The physics of a CT from my brief research states that,/"...the 
> secondary of a current transformer should not be disconnected from its 
> burden while current is in the primary, as the secondary will attempt 
> to continue driving current into an effective infinite impedance 
> potentially generating high voltages and thus compromising operator 
> safety." /This begs the question how I can use my DMM clamp meter w/o 
> causing damage or is the italicized text related to very high current 
> applications from the world of medium and high voltage equipment and 
> not as pertinent to the residential and light commercial world I work in?
>
> I suspect this is a no-brainer answer for the seasoned professionals 
> on the list and I'll be most appreciative for any proof (no matter how 
> brief) you wish to share.  Ultimately we wish to minimize the need to 
> perform power shut downs and interrupt client service when installing 
> load monitoring CTs to a home but only wish to do so if it is part of 
> a safe and non equipment-harming process.
>
> Sincerely,
> Sam Haraldson
>
> OnSite Energy 
> <https://www.google.com/url?q=https://onsiteenergyinc.com/&source=gmail-html&ust=1677085494759000&usg=AOvVaw2NN36GoM1sjnS4RdC8Svt-> 
> 	
> SAM HARALDSON
> Field Operations Director
> (406) 551-6135
> 1515 N. Rouse Ave Bozeman, MT 59715
> Locally owned and operated since 2012
> 	B Corporation 
> <https://www.google.com/url?q=https://onsiteenergyinc.com/bcorp&source=gmail-html&ust=1677085494759000&usg=AOvVaw0EluC1lXtz2KlRFag-htKe> 
>
>
>
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