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Old 07-19-2015, 08:45 AM   #1
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Default Ac loop impedance testing

Ac loop impedance testing

Methinks this article is a tad confusing, if not outright misleading

I'd like to ask some of you UK sparks to unfuzz us, as i'm aware you're far more up on the topic

thx

~CS~
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Old 07-19-2015, 04:20 PM   #2
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I am not from the UK, but I am part Irish.

It appears you only test below 50 amps. Then anything over 50 amps you calculate.

http://www.w.mylocalelectrician.co.u...your-meter-lie
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Old 08-11-2015, 04:48 AM   #3
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Quote:
Originally Posted by chicken steve View Post
Ac loop impedance testing

Methinks this article is a tad confusing, if not outright misleading

I'd like to ask some of you UK sparks to unfuzz us, as i'm aware you're far more up on the topic

thx

~CS~
Hi Steve
Fault loop impedence testing ,is. Just measuring the. Fault current paths resistance to ensure its low enough for the protection device ie circuit breaker trips.
Here in Oz we have. Two tables which we reference to, one is for live testing using a fault loop impedence tester and the other table is for dead testing. Which youncan use a digital multimeter. You lift the earth of. Say at the load end and short it to the hot wire and back at the switchboard you measure the resistance between the hot wire and earth. The reason for lifting the earth of. Is to ensure no parallel paths exist..hope that makes sense.
There are some good videos UK based on youtube by a guy called Chris Kitcher check them out.
HTH
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Old 08-11-2015, 05:43 AM   #4
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Thx Frank

So what would be the dif if we lift our GEC's , and used a megger here?

~CS~
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Old 08-12-2015, 02:42 AM   #5
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Thx Frank

So what would be the dif if we lift our GEC's , and used a megger here?

~CS~
Hi Steve
your meggar would be used to measure the insulation resistance not fault loop impedence,unless your. Meggar can also measure low resistance???
The video you linked to was.a Fault loop impedence of the mains cable back to the substation known as Ze ( I believe)
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Old 08-12-2015, 03:52 AM   #6
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Ze would be correct (e I think stands to 'external')
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Old 09-03-2015, 01:23 PM   #7
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Earth loop testing has become more troublesome with the massive rollout of rcbo type breakers this means the loop test is carried out using only 15ma so as not to trip a 30ma rcbo. Imagine pushing 15ma round from the outlet you are testing from all the way to the transformer and back, the readings can vary terribly by as much as 1 ohm.
with no rcbo in place and just an mcb we use a different scale which pushes more current through and is more accurate and quicker. 1-2 seconds instead of 10seconds.
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Old 09-03-2015, 06:29 PM   #8
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High current test is always more accurate from what Ive heard. Cant you get away with 30ma RCBOs?
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Old 09-04-2015, 01:25 AM   #9
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Yep the rcbos are 30 ma it's the tester that only puts 15 ma down the cable I have a Megger 1720 multi function tester they cost about £700 including our VAT.
What sort of testers are common in the U.S. is there a brand that is most popular. We tend to use Megger/avo or fluke.
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Old 09-04-2015, 11:26 AM   #10
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Quote:
Originally Posted by mrmarksparks View Post
Yep the rcbos are 30 ma it's the tester that only puts 15 ma down the cable I have a Megger 1720 multi function tester they cost about £700 including our VAT.
What sort of testers are common in the U.S. is there a brand that is most popular. We tend to use Megger/avo or fluke.

Earth fault loop impedance testing isnt done in the US, but when it comes to volt meters/clamp on amp meters ect Fluke is very common.


Megger seems to be the most common when insulation resistance testing is done.

Do you have a link to your Fluke multi function testers?
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Old 09-04-2015, 12:22 PM   #11
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http://isswww.co.uk/fluke-1652c-17th...xQ9RoCRB_w_wcB

This is the instrument our engineers use.
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Old 09-04-2015, 12:40 PM   #12
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Quote:
Originally Posted by mrmarksparks View Post
http://isswww.co.uk/fluke-1652c-17th...xQ9RoCRB_w_wcB

This is the instrument our engineers use.

Dont sparkies also use those day to day? I've been thinking of getting one but unsure how those tester will like 120 volts 60Hz.
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Old 09-04-2015, 01:10 PM   #13
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We all have a multifunction tester each of like that or the Megger equivalent used mainly for testing our own new installations or fault finding.
We also carry out a lot of electrical installation condition reports (5 yearly)
Inspections on commercial property's schools , offices etc.

http://www.eyre-electrical-mechanical.co.uk

The link is to the website of the company I work for.
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Old 09-05-2015, 07:23 AM   #14
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Quote:
Originally Posted by mrmarksparks View Post
Earth loop testing has become more troublesome with the massive rollout of rcbo type breakers this means the loop test is carried out using only 15ma so as not to trip a 30ma rcbo. Imagine pushing 15ma round from the outlet you are testing from all the way to the transformer and back, the readings can vary terribly by as much as 1 ohm.
with no rcbo in place and just an mcb we use a different scale which pushes more current through and is more accurate and quicker. 1-2 seconds instead of 10seconds.

Well i see there are many different abbreivations for types of breakers manufactured and installed off my turf>>>


http://www.rcd-rcbo.com/

Quote:
Ezitown,founed in 2005,A Professional manufacturer of Circuit breaker,mcb,mccb,elcb,rccb,rcd,rcbo etc. which are exported to all over theworld. As an ISO 9001:2008 certified company we are always keeping our supply with high quality products at competitive price
If I can i take it they all employ some sort of torodial coil , i get why 1 ohm can be a problem

As we (American NEC & Canadian CEC) seem to be stumbling along with our our version of this coil philosophy (however hackish it may be) , i would imagine the testing(s) would follow suit as well.....?

Best i can do, am trained in & know is to meg out circuitry.....
Why aren't we doing EFL testing here?

~CS~
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Old 09-05-2015, 07:31 AM   #15
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24 string temporary light set,
24 100 watt lamps
=
20amp load test.
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Old 09-05-2015, 09:03 AM   #16
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Quote:
Originally Posted by chicken steve View Post
Well i see there are many different abbreivations for types of breakers manufactured and installed off my turf>>>


http://www.rcd-rcbo.com/



If I can i take it they all employ some sort of torodial coil , i get why 1 ohm can be a problem

As we (American NEC & Canadian CEC) seem to be stumbling along with our our version of this coil philosophy (however hackish it may be) , i would imagine the testing(s) would follow suit as well.....?

Best i can do, am trained in & know is to meg out circuitry.....
Why aren't we doing EFL testing here?

~CS~
Its interesting, earth fault loop impedance testing and mag trip provide arc fault protection as claimed by NRTLs and the CMP:




Quote:
The UL report states “breakers can be effective at mitigating arcing faults, provided the available fault current can be guaranteed to exceed the magnetic trip level of the circuit breaker by a factor of 1.25.”

The function of UL489e (supplemental arc breaker):



Quote:
(b)The branch circuit breaker shall be listed and marked as having an
instantaneous trip not exceeding 300 amperes.

Quote:
This proposal establishes a circuit breaker
listing and marking requirement for the magnetic trip level at or below 300A in order to ensure the breaker will protect the circuit from a parallel arcing fault when at least 500A of available fault current is present as required in the first
parameter.
Quote:
LAROCCA, R.: While we support the panel action, continued support is
dependent upon review of additional data that would confirm the availability of
sufficient short circuit current capability at the panel of a typical installation.
The arc fault protection of the branch circuit will be provided by a system
that includes an outlet branch circuit AFCI, a circuit breaker having a knowninstantaneous trip current and a branch circuit of a limited length and resistance to ensure that the fault current is sufficient to trip the breaker during a parallel arcing fault at the installation point of the outlet branch circuit AFCI. The latest UL Research Report takes into consideration the impact of the available current at the panel on the acceptable length of the branch circuit home run to the first outlet. Calculation shows that as the available current at the origin of the branch circuit varies, so does the allowable length of the home run. Additional study is needed to provide data regarding the current available at the origin of the branch circuit in a typical installation. From this data, the panel will be able to determine if modification of the panel action should be considered at the ROC.
Quote:
The report focused on providing data on the performance of conventional circuit breakers with respect to arc faults in the home run portion of the branch circuit and identified the parameters that must be met and controlled for this tohappen. As long as these parameters are controlled, it can be concluded that an outlet branch circuit type arc-fault circuit interrupter could possibly be used in conjunction with a low-magnetic type circuit breaker to protect the branchcircuit. The critical parameters summarized in the report include: a minimum available fault current, a maximum magnetic trip level for the circuit breaker, impedance of the conductor, the actual voltage and the length of the conductor.This proposal is based on utilizing the parameters set forth by the UL Report to revise 210.12 to permit using an outlet branch circuit arc-fault circuit interrupter in conjunction with a low magnetic trip circuit breaker.




Quote:
(2) A listed outlet branch circuit type arc-fault circuit interrupter installed at the first outlet on the branch circuit where all of the following conditions aremet:

(a) The branch circuit over current protection device shall be a listed circuitbreaker having an instantaneous trip not exceeding 300 amperes.


Quote:
(2) A listed outlet branch circuit type arc-fault circuit interrupter installed at the
first outlet on the branch circuit where all of the following conditions are met :
(a) The available fault current at the branch circuit overcurrent device shall not
be less than 500A and the ambient temperature shall not be less than 20°C
(68°F).
(b)The branch circuit breaker shall be listed and marked as having an
instantaneous trip not exceeding 300 amperes.

© The branch circuit wiring shall be continuous from the branch circuit
overcurrent device to the outlet branch circuit arc-fault circuit interrupter.
(d) The maximum length of the branch circuit wiring from the branch circuit
overcurrent device to the first outlet shall be determined using the following:
L = (0.4×Vrms) / (1.25×300×pL)
L is the maximum length of the “home run” in feet;
pL is the resistivity per unit foot of each conductor of the NM cable gauge
being used; and
Vrms is the actual supply voltage.




Can be found here starting at page 70-129 (139 in the viewer):


https://www.nfpa.org...0-A2013-ROP.pdf


Somehow I sense that the British take this for granted.

Mind you we are talking proposals for 300amps. An established 150 amp OCPD will provide arc fault protection to 125 feet of NM in most applications. Its ironic they rejected this same concept for branch feeder AFCIs in 1999, yet revisiting it only when the same function is needed after series arc protection is already made mandatory.
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Old 09-05-2015, 12:02 PM   #17
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Meadow,
I'm compelled to ask.....

what is the advantage of lower mag trips ?

in fact...

what are the disadvantages ?

~CS~
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Old 09-05-2015, 12:13 PM   #18
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Quote:
Originally Posted by chicken steve View Post
Meadow,
I'm compelled to ask.....

what is the advantage of lower mag trips ?

in fact...

what are the disadvantages ?

~CS~
Low mag trip is cheaper, far more reliable and contains no electronics to fail. It drastically reduces the incident energy at any fault, and NRTL testing has shown it mitigate arc faults better then electronics.

Two disadvantages:

1. Mag trip that is to low can trip on large motors or high inrush appliances.

2. In some cases it maybe necessary to consider fault current in the circuit if you want to grantee ever point in the circuit can trip the breaker magnetically. (Earth fault loop impedance).

Any way, just to give you an idea of what magnetic trip vs thermal trip looks like on a fault consider the breaker trip times here:


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Old 09-06-2015, 11:53 AM   #19
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[quote=meadow;2237897]
Quote:
Low mag trip is cheaper, far more reliable and contains no electronics to fail. It drastically reduces the incident energy at any fault, and NRTL testing has shown it mitigate arc faults better then electronics.





Quote:
Two disadvantages:

1. Mag trip that is to low can trip on large motors or high inrush appliances.

2. In some cases it maybe necessary to consider fault current in the circuit if you want to grantee ever point in the circuit can trip the breaker magnetically. (Earth fault loop impedance).

So if fault currents in a system with unknown impedance can cause incendiary events , lowering the mag trip levels AND verifying said impedance would be prudent, am i close....?




Quote:
Any way, just to give you an idea of what magnetic trip vs thermal trip looks like on a fault consider the breaker trip times here:
The thermal smoked @ 11 seconds there. I guess that also serves as a good Ac/Dc example , for any of us delving into photovoltaics.

~CS~
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Old 09-06-2015, 12:33 PM   #20
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Quote:
Originally Posted by chicken steve View Post


So if fault currents in a system with unknown impedance can cause incendiary events , lowering the mag trip levels AND verifying said impedance would be prudent, am i close....?
Thats correct. Anytime a breaker can trip magnetically during a fault incident energy and wire stress (thermal and magnetic) is greatly reduced.




Quote:
The thermal smoked @ 11 seconds there. I guess that also serves as a good Ac/Dc example , for any of us delving into photovoltaics.

~CS~
The breaker did smoke because its interrupting DC, however the DC was able to prevent the solenoid from activating.

Keep in mind IEC miniature breakers have 2 parts, a bimetlic strip for overloads and a solenoid coil for short circuits:

https://www.google.com/search?q=insi...QaRcqLq3s1M%3A
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