UK What kind of resistor as there are so many?

[Rather be Fishing]

Hello and thanks for taking
a look at my question.

Basically I am struggling to source some resitors that I need to connect into a circuit so my instrument can read realistic measurements on a small rig.

I need 1ohm, 2ohm, and some 0.5ohm, 0.2ohm and 0.1ohm resistors.

When I ring RS they say that they have thousands of different types and need more information.

When I type them sizes into eBay I'm left perplexed on what would be the right purchase

I've got some one who said they help me install them but I don't want to keep asking him stupid questions as I've already asked him what size resistors to get and was called needy ? so I don't want to push my luck.

If anyone knows what it is I need to be asking for would you mind telling me so I can order them please?

Thank you for any help

 

[SparkyChick]

I'm afraid you're going to need to be a bit more specific.

Two of the key issues are power dissipation and voltage rating. You mention a 'rig', so if these are being inserted into cabling to simulate longer cabling and you're planning on insulation resistance testing them, you obviously can't use small scale parts as they could be prone to arcing. Likewise, if you're going to connect this to the mains for live testing... Zs for example, they may need to be able to handle some larger currents (particularly if you can use a 2 lead EFLI test - which is more reliable than a 3 lead as it uses higher currents, the same applies to continuity readings with an MFT which can be much higher current than those conducted using a multimeter).

So, you'll need to provide more detailed information.

If they are to be used as I've described above, I would probably use the metal clad high power resistors that are rated to at least 600v.

 

[pc1966]

As above, critical information is:

• Operating power from I^2*R
• Operating voltage (for high R where power less of an issue, and for isolation to nearby objects)
• Tolerance (i.e. accuracy)
• Fixing method (for example surface mount parts are very difficult to impossible to hand solder, so you are looking at either leaded / "through-hole" style, or the metal ones with solder lugs that @SparkyChick mentioned)

 

[Rather be Fishing]

I'm afraid you're going to need to be a bit more specific.

Two of the key issues are power dissipation and voltage rating. You mention a 'rig', so if these are being inserted into cabling to simulate longer cabling and you're planning on insulation resistance testing them, you obviously can't use small scale parts as they could be prone to arcing. Likewise, if you're going to connect this to the mains for live testing... Zs for example, they may need to be able to handle some larger currents (particularly if you can use a 2 lead EFLI test - which is more reliable than a 3 lead as it uses higher currents, the same applies to continuity readings with an MFT which can be much higher current than those conducted using a multimeter).

So, you'll need to provide more detailed information.

If they are to be used as I've described above, I would probably use the metal clad high power resistors that are rated to at least 600v.

Cheers for your dropping in SparkyChic

Basically I've put myself onto the 2392 -52 and im feeling a bit out of my depth. I've already taken the plunge so I'm going to see it through to the end as it will stand me in good stead going foward if I need to retake it.

Because of that I've decided to try and help myself by building a rig to practise on as I don't do any inspection or testing for my Job.

I did try to get a picture of a suitable rig to build at home but was told it sails a bit close to the wind in terms of cheating/breaching the C&G rules if I was to be provided that which is fair enough. So I'm just gonna build one similar to those I've seen on the internet, take a pic and see what he thinks. Hopefully see what he thinks .
I got told if I buy big bag of resistors from RS or ebay I can draw you up or make suggestions as to a suitable set up that will help you.

Which is mega decent of him.

I went on eBay and was left bamboozled,so I rang us RS instead and they said I needed to be more specific as they had over 90 thousand resistors in there catalogue.

So I want back to the guy I'm a pain in the --- to and was told

Think circuits - 1ohm, 2ohm, and some 0.5ohm, 0.2ohm and 0.1ohm resisters to connect in circuit so your instrument can read realistic measurements on a small rig.

Packs of10 are cheap as chips on ebay.

I went back to eBay and typed them sizes in and was left confused as to what I word be getting as some said the contents of the packs were random and unknown ?

So I called RS back up knowing the resistor sizes and they said I need to be more specific then that.

I'm reluctant to go back to this chap as he has already said I am needy ? but he's such a knowledgeable chap I could do with finding these resistors

 

[Rather be Fishing]

As above, critical information is:

• Operating power from I^2*R
• Operating voltage (for high R where power less of an issue, and for isolation to nearby objects)
• Tolerance (i.e. accuracy)
• Fixing method (for example surface mount parts are very difficult to impossible to hand solder, so you are looking at either leaded / "through-hole" style, or the metal ones with solder lugs that @SparkyChick mentioned)

Cheers for dropping in @pc1966. Appreciate it.

Going on what you two have just said and the fact that I was told they are only cheap for packs of 10 I think it's either like you and @SparkyChick say, a through hole style one or the metal ones with solder lugs. Not that I new that before.

I'll ring RS back armed with that new information.

Thanks alot you two ?

 

[pc1966]

This will give you an idea of the options for a 1 ohm resistor on RS:

Through Hole Resistors | Carbon Film | RS

Through hole fixed resistors reduce the flow of current in circuits and are attached via leads inserted into the holes of printed circuit boards.

uk.rs-online.com

 

[Rather be Fishing]

This will give you an idea of the options for a 1 ohm resistor on RS:

Through Hole Resistors | Carbon Film | RS

Through hole fixed resistors reduce the flow of current in circuits and are attached via leads inserted into the holes of printed circuit boards.

uk.rs-online.com

Thank you @pc1966 ?

 

[SparkyChick]

All I'm going to say is this... every circuit simulation I've seen for this purpose or similar has used high power high voltage metal clad resistors for the reasons I've outlined above.

 

[Rather be Fishing]

All I'm going to say is this... every circuit simulation I've seen for this purpose or similar has used high power high voltage metal clad resistors for the reasons I've outlined above.

Thanks for your advise @SparkyChick it's appreciated ?

 

[pc1966]

The equivalent sort of RS search for those:

Chassis Mount Resistors | Panel Mount Fixed | RS

Reduce the flow of electricity in your electrical circuit to avoid damage or destruction of your circuit components with a panel mount fixed resistor.

uk.rs-online.com

 

[Lucien Nunes]

Please explain exactly what the resistors are going to be used for. E.g. 'Simulating high resistance connections using continuity tests with an MFT.' That would help us guide you towards the correct type of part by estimating the power and voltage requirements.

There are indeed many kinds of resistor, I keep over 1000 types in stock over my workbench just for basic day-to-day activities.. To give you an example of how the construction varies, the picture shows three 4.7 ohm resistors that I had within arm's reach:
300W Aluminium-clad wirewound
1W Metal oxide film axial
0.25W Metal film SMD 1206 (at the end of the biro)

 

[marconi]

resistors | Rapid Online - https://www.rapidonline.com/Catalogue/Search?Query=resistors&Size=20&Tier=Aluminium%20Clad

Have a look at this link. Select your resistance value and then filter to find some products. I suggest you use these aluminium clad resistors because they are robust, high power and can be easily secured in your rig. You can practice soldering to the ends and may want to buy some crocodile clips so you can connect them into circuits.

You could buy 1 Ohm for the 1 Ohm, 2 Ohm, 3 Ohm and two in parallel would be the 0.5Ohm.

Then buy some 0.5Ohms and then two in parallel provides 0.25 Ohms etcetera.

But you may prefer to have single resistors so look them up.

Looking at the thickness of the test leads of a METREL I think the maximum test current will be circa 10A so the power value of the resistor is IsquaredR. Thus for 3 Ohm it needs to have a power rating of 10 x 10 x 3 = 300Watts. But as the tests only take at most a few seconds I would buy 50W resistors which are cheaper and I reckon will suit your purpose.

 

[marconi]

I have 3.3R 25W x 6 and 5.6R 6W x 3 which you may have for free.

Just PM me your name and address and I will post them tomorrow.

 

[Rather be Fishing]

i

Please explain exactly what the resistors are going to be used for. E.g. 'Simulating high resistance connections using continuity tests with an MFT.' That would help us guide you towards the correct type of part by estimating the power and voltage requirements.

There are indeed many kinds of resistor, I keep over 1000 types in stock over my workbench just for basic day-to-day activities.. To give you an example of how the construction varies, the picture shows three 4.7 ohm resistors that I had within arm's reach:
300W Aluminium-clad wirewound
1W Metal oxide film axial
0.25W Metal film SMD 1206 (at the end of the biro)

View attachment 64414

Thanks for dropping in @Lucien Nunes and taking the trouble to show me some of the different types of resistors out there.

I thought the one at the top of the biro was the one on the wire. It wasn't untill I zoomed to the pic I realised there was another one there like you said.

Thank you mate ?

 

[Rather be Fishing]

resistors | Rapid Online - https://www.rapidonline.com/Catalogue/Search?Query=resistors&Size=20&Tier=Aluminium%20Clad

Have a look at this link. Select your resistance value and then filter to find some products. I suggest you use these aluminium clad resistors because they are robust, high power and can be easily secured in your rig. You can practice soldering to the ends and may want to buy some crocodile clips so you can connect them into circuits.

You could buy 1 Ohm for the 1 Ohm, 2 Ohm, 3 Ohm and two in parallel would be the 0.5Ohm.

Then buy some 0.5Ohms and then two in parallel provides 0.25 Ohms etcetera.

But you may prefer to have single resistors so look them up.

Looking at the thickness of the test leads of a METREL I think the maximum test current will be circa 10A so the power value of the resistor is IsquaredR. Thus for 3 Ohm it needs to have a power rating of 10 x 10 x 3 = 300Watts. But as the tests only take at most a few seconds I would buy 50W resistors which are cheaper and I reckon will suit your purpose.

Thank you for dropping in as well @marconi and taking the time to reply. I'm very grateful for you advice and help in directing me to that link.

Thank you ?

 

[Rather be Fishing]

Just wanted to say thank you to everyone who has helped me out with my question.

It's very decent of all of you to take some time out of your day to do so.

Cheers ??

 

[Lister1987]

Power resistors are what you're after ircc, our test rigs at college have them and they ain't cheap

 

[Lister1987]

Cheers for dropping in @pc1966. Appreciate it.

Going on what you two have just said and the fact that I was told they are only cheap for packs of 10 I think it's either like you and @SparkyChick say, a through hole style one or the metal ones with solder lugs. Not that I new that before.

I'll ring RS back armed with that new information.

Thanks alot you two ?

Wire them via a bank of grid switches so you can easily switch them in and out

 

[marconi]

I asked Megger at Dover about the currents which circulated when one of their MFT's is used. A very helpful reply which I can summarise as:

1. To comply with BS7671 the current is at least 200mA during continuity tests;

2. During high voltage insulation tests the current is about 1mA;

3. During two-wire high current loop tests the current is about 20A in older MFTs and about 5A for newer models - these tests only last milli-seconds so the Ohmic heating (IsquaredR) in any test resistor will be negligible.

The resistor power ratings I have recommended will therefore be suitable.

 

[Rather be Fishing]

Thank you @marconi
?