Ohms range question

[PetrosA]

This is something I've been thinking about for a while since I got a new clamp meter this year. Although it's not a cheap meter, it's resistance range tops out at 4 kOhms. It was the one spec I didn't think to check since my last clamp meter did everything I needed.

So my question is this - what tests do you do that would normally require more than 4 kOhms range? The one thing I know I need it for is checking floor heat thermistors which generally read between 8 and 12 kOhms, but this seems well below the ranges I'm seeing on some Ideal, Klein or Greenlee clamps which have advertised ranges anywhere from 20 MOhms to 50 MOhms. Where am I going to need that range?

 

[dereckbc]

So my question is this - what tests do you do that would normally require more than 4 kOhms range? The one thing I know I need it for is checking floor heat thermistors which generally read between 8 and 12 kOhms,

Well I was going to say you shouldn't need anything higher as with most electrical work is verifying continuity. Only other thing I can think of is testing capacitors, which is better done with an ole fashion analog meter with a pointer.

 

[hurk27]

I have a Amprobe 610 AC/DC which I have grown fond of.

While it's not the most accurate meter it's close (as long as the battery is good)

the main thing I like is being able to check the frequency of generators output, and the fact it measures DC current up to 750 amps for one minute, which will allow me to check starting current and alternator output.

The one thing that bugs me is, if the battery gets below 6 volts it will start reading higher then what the real voltage is, but there is a battery warning icon in the display (that I forget to check):roll:

It to has only a 4k ohm meter, which is ok for the most part as anything above that come up very rarely, if it does I have 40 meg Flukes in the truck also, and a megger that has a .0 ohm range for less then one ohm for testing FOP across breakers and other connections.


Here is a link to the manual of the 610 with the schematics and the calibration instructions:
ACDC610.pdf

it was a lucky find at a yard sale back in 1998 along with finding a greenlee wire tracer.

Paid $15.00 for the 610 retail in 1998 was $685.00
Paid $20.00 for the greenlee wire tracer live or dead tracing
retail back then was $825.00

Both were brand new in box never used.

Best yard sale I ever went to.

 

[wptski]

That Amprobe 610 lists a input impedance of 10M but many clamp meters are only around 1M including all Fluke models. That 1M isn't low enough to eliminate "ghost" voltage.

 

[ptonsparky]

Meters with low resistance scales such as yours are a almost useless when it comes to finding problems with GFCIs, AFCIs, motors and faulted underground wires. Add a megger to your toolbox and your set.

A customer had a kitchen GFCI tripping occasional. He had replaced it once. Handy dandy T-Pro would not indicate a fault. Megger nailed it first time. New siding.

 

[nhfire77]

So my question is this - what tests do you do that would normally require more than 4 kOhms range?

Ground Faults on low voltage systems, specifically fire alarms, most panels with see up to 40k to ground as a fault.

Burg end of line resistors i.e. bosch POPITS have as 33K ohm resistor.

Firelite Addressable Input modules have a 47K ohms resistor.

Silent Knight EOL is 4.7K Ohms.

I will stop there.

 

[tx2step]

This is something I've been thinking about for a while since I got a new clamp meter this year. Although it's not a cheap meter, it's resistance range tops out at 4 kOhms. It was the one spec I didn't think to check since my last clamp meter did everything I needed.

What meter did you buy?

 

[PetrosA]

Thanks for the responses. I bought an Agilent U1211A which is the cheapest of the three clamp meters they sell, but at $250 it isn't cheap as clamp meters go. Only their top-of-the-line model U1213A goes above 4 kOhms. Their regular DMMs are very nice though and they came out with a line of industrial grade DMMs that easily rival the Fluke 87 and 82 and they're working on an Ex line for hazardous locations.

The reason I posted this question is because I had the opportunity to meet with three of their people last week from the industrial handheld division which is in Malaysia. We had a three hour meeting and that was one of the things I brought up as something in need of an upgrade. My examples of when you need more range was limited to my own experience though. I'll pass on what I get here.

It's interesting that someone mentioned meggers. I have one, but on the regular ohms setting (no voltage stress testing) it only goes to a few hundred ohms so it's useless for things like the thermistor test. Do newer ones have a higher range on the regular resistance setting?

 

[ptonsparky]

I don't have it my hands, but I think 22k for my my Fluke 1507. At least that is What it scales.out Max on opens.

 

[dbuckley]

My DMM I think goes to 30M ohms, but its a low voltage low current test. I have a megger and a multi-purpose tester that both go up to half a gig ohms (500M) with test voltages from 50V to 1000V, and the multi-tester can do a high current (well, realtively, 200mA) for low resistance testing. The multi-tester can also figure out ground loop resistance from an operating circuit.

Between that lot I can figure out the resistance of most things encountered in the electrical world

 

[PetrosA]

My DMM I think goes to 30M ohms, but its a low voltage low current test. I have a megger and a multi-purpose tester that both go up to half a gig ohms (500M) with test voltages from 50V to 1000V, and the multi-tester can do a high current (well, realtively, 200mA) for low resistance testing. The multi-tester can also figure out ground loop resistance from an operating circuit.

Between that lot I can figure out the resistance of most things encountered in the electrical world

I ended up getting a Greenlee DM810 on ebay just for the higher ohms readings I needed plus it does basic datalogging as well. Interestingly there isn't anything like your installation tester available in the US that I know of. From what I see Fluke and others only make them for testing to IEC conformance but not any US standards.

 

[Jlarson]

I prefer meters that have a high ohm range. Partly because I do some board level stuff and instrumentation but also cause I like to use ohms to put starter controls and relay logic through its paces before I power it up.

It's a habit I picked up when I first stated out from someone I learned from, it's nice to figure out that you accidentally wired that start push button across phases before you turn the power on and try it for real. Hey, I'm not perfect and occasionally make mistakes just like everyone else.

 

[dbuckley]

Interestingly there isn't anything like your installation tester available in the US that I know of. From what I see Fluke and others only make them for testing to IEC conformance but not any US standards.

I too find some puzzlement on this.

The NEC gives chapter and verse on exactly how an installation may (and may not) be assembled, but it is ASSumed that once its built "to code" and inspected then it's perfect and safe.

In the jurisdictions I've worked in, electrical test as proof of compliance is required. The test gear I use would work perfectly well in the USA, but there are no specifications that you could test to.

I'm a big fan of testing; building a perfectly code compliant installation is one thing, but having a rocker bust it invisibly (accidently and unknowingly - no malice implied) with his sawzall is something else altogether.

 

[iwire]

The NEC gives chapter and verse on exactly how an installation may (and may not) be assembled, but it is ASSumed that once its built "to code" and inspected then it's perfect and safe.

I disagree the NEC suggests that at all. The first sections of the NEC tell us the NEC alone may not be enough and that we need to look elsewhere for design information.

90.1 Purpose.

(A) Practical Safeguarding. The purpose of this Code is
the practical safeguarding of persons and property from
hazards arising from the use of electricity.

(B) Adequacy. This Code contains provisions that are considered
necessary for safety. Compliance therewith and
proper maintenance results in an installation that is essentially
free from hazard but not necessarily efficient, convenient,
or adequate for good service or future expansion of
electrical use.

FPN: Hazards often occur because of overloading of wiring
systems by methods or usage not in conformity with
this Code. This occurs because initial wiring did not provide
for increases in the use of electricity. An initial adequate
installation and reasonable provisions for system
changes provide for future increases in the use of
electricity.

(C) Intention. This Code is not intended as a design specification
or an instruction manual for untrained persons.

(D) Relation to Other International Standards. The requirements
in this Code address the fundamental principles
of protection for safety contained in Section 131 of International
Electrotechnical Commission Standard 60364-1,
Electrical Installations of Buildings.

In the jurisdictions I've worked in, electrical test as proof of compliance is required. The test gear I use would work perfectly well in the USA, but there are no specifications that you could test to.

We often do jobs where the specifications require us, or a third party too perform a list of tests and produce reports to the engineers satisfaction.

A common requirement is insulation testing of circuits 100 amps and larger, providing detailed reports of each test and the conditions the test was done under.

Other types of testing might be IR scans or grounding system testing.

I'm a big fan of testing; building a perfectly code compliant installation is one thing, but having a rocker bust it invisibly (accidently and unknowingly - no malice implied) with his sawzall is something else altogether.

I am big fan of doing what I am paid to do so if the specs require testing I am all for it. But I would hate to see a sudden change in the NEC without clear evidence the change is needed.