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

[Sam Haraldson via RE-wrenches]

A quick note of thanks to the wide variety of responses I received last
week regarding my question about safely clamping CTs around live
conductors.  I genuinely appreciate the supportive responses.

Sincerely,
Sam

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

[Jason Szumlanski via RE-wrenches]

I have installed many hundreds of Enphase CTs on live service conductors.
As long as the secondary is connected first, no problem. Same with
disconnecting them.

Jason


On Fri, Mar 8, 2024, 11:30 AM Sam Haraldson via RE-wrenches <
re-wrenches@lists.re-wrenches.org> 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
>
> [image: OnSite Energy]
> 
>
> SAM HARALDSON
> Field Operations Director
> (406) 551-6135
> 1515 N. Rouse Ave Bozeman, MT 59715
> Locally owned and operated since 2012
> [image: B Corporation]
> 
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Re: [RE-wrenches] Clamping CTs Around Live Conductors - White Paper References and/or Anecdotal Information Requested

[Kent via RE-wrenches]

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 
 
	

SAM HARALDSON
Field Operations Director
(406) 551-6135
1515 N. Rouse Ave Bozeman, MT 59715
Locally owned and operated since 2012
	B Corporation 
 




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

[Glenn Burt via RE-wrenches]

The answer depends on the type of CT.If it has an internal resistor which 
converts the measuerment to a voltage, it is okay to clamp on live.If it is 
purely a CT that outputs a different current to be measured, then they can 
create an inductive kick ant shock and destroy.-GlennSent from my 'smart'phone, 
so please excuse typos and spelling errors.-- Original message--From: 
Sam Haraldson via RE-wrenchesDate: Fri, Mar 8, 2024 11:29 AMTo: RE-wrenches;Cc: 
Sam Haraldson;Subject:[RE-wrenches] Clamping CTs Around Live Conductors - White 
Paper References and/or Anecdotal Information RequestedDear 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  SAM HARALDSON  Field 
Operations Director(406) 551-61351515 N. Rouse Ave Bozeman, MT 59715Locally 
owned and operated since 2012
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Re: [RE-wrenches] Clamping CTs Around Live Conductors - White Paper References and/or Anecdotal Information Requested

[Blake Gleason via RE-wrenches]

Hi Sam,

The "secondary" of the CT is the side connected to the meter.  The primary
is the side that gets wrapped around the conductor or busbar on which you
are measuring current.  So yes, make sure that the secondary is connected
to its "burden" (the meter, or a shorting block) before inducing any
current in the primary.  With a split-core CT, or a handheld clamp meter
(as you noted), you can install the CT around a conductor while the
conductor is in service.  Just make sure the secondary is already
connected.  (I'm sure there is some exception for certain types of
sensitive meters, but I've never had a problem.  And yes, as you say, this
is assuming that you are using proper PPE, etc for working around live
circuits.)

Blake


On Fri, Mar 8, 2024 at 8:31 AM Sam Haraldson via RE-wrenches <
re-wrenches@lists.re-wrenches.org> 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
>
> [image: OnSite Energy]
> 
>
> SAM HARALDSON
> Field Operations Director
> (406) 551-6135
> 1515 N. Rouse Ave Bozeman, MT 59715
> Locally owned and operated since 2012
> [image: B Corporation]
> 
> ___
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-- 

Blake Gleason, PE | Employee Owner
Director of Innovation and Technical Excellence
O: 510-845-2997 x128
C: 510-867-5878

1035 Folger Ave.
Berkeley, CA 94710
www.sunlightandpower.com
License #326203

 

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

[Darryl Thayer via RE-wrenches]

I have done it many times. YES terminate the secondary first.  As an older
CT is a step up the voltage transformer and can generate thousands of
volts.  Many of new type Cats are low voltage output and are safe to work
with.

On Fri, Mar 8, 2024, 10:46 AM Jerry Shafer via RE-wrenches <
re-wrenches@lists.re-wrenches.org> wrote:

> Wrenches
> Per manufacturer recommended installation procedures you must have the CT
> terminated befor the load connection can made and yes this can damage the
> CT. Depending on what you are connecting to there may also be a "short pin"
> to prevent component damage so keep that in mind when commissioning a
> logger.
> Regarding your question about hand heldsi have seen failures of cheaper
> units, l have Flukes and never had an issue with them
> Fun times
>
> On Fri, Mar 8, 2024, 8:30 AM Sam Haraldson via RE-wrenches <
> re-wrenches@lists.re-wrenches.org> 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
>>
>> [image: OnSite Energy]
>> 
>>
>> SAM HARALDSON
>> Field Operations Director
>> (406) 551-6135
>> 1515 N. Rouse Ave Bozeman, MT 59715
>> Locally owned and operated since 2012
>> [image: B Corporation]
>> 
>> ___
>> List sponsored by Redwood Alliance
>>
>> Pay optional member dues here: http://re-wrenches.org
>>
>> List Address: RE-wrenches@lists.re-wrenches.org
>>
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Re: [RE-wrenches] Clamping CTs Around Live Conductors - White Paper References and/or Anecdotal Information Requested

[Jerry Shafer via RE-wrenches]

Wrenches
Per manufacturer recommended installation procedures you must have the CT
terminated befor the load connection can made and yes this can damage the
CT. Depending on what you are connecting to there may also be a "short pin"
to prevent component damage so keep that in mind when commissioning a
logger.
Regarding your question about hand heldsi have seen failures of cheaper
units, l have Flukes and never had an issue with them
Fun times

On Fri, Mar 8, 2024, 8:30 AM Sam Haraldson via RE-wrenches <
re-wrenches@lists.re-wrenches.org> 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
>
> [image: OnSite Energy]
> 
>
> SAM HARALDSON
> Field Operations Director
> (406) 551-6135
> 1515 N. Rouse Ave Bozeman, MT 59715
> Locally owned and operated since 2012
> [image: B Corporation]
> 
> ___
> List sponsored by Redwood Alliance
>
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[RE-wrenches] Clamping CTs Around Live Conductors - White Paper References and/or Anecdotal Information Requested

[Sam Haraldson via RE-wrenches]

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

[image: OnSite Energy]


SAM HARALDSON
Field Operations Director
(406) 551-6135
1515 N. Rouse Ave Bozeman, MT 59715
Locally owned and operated since 2012
[image: B Corporation]

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