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george258

Hello & help with AM2

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george258

Hi, 


This is my first post, although I have been browsing the forums for a little while now. 

I work in BMS and have my AM2 on friday. The nature of my work means I don't get to test so there are a few things I'm unsure of and was hoping for some clarification. 
I know for some people they may be obvious but I don't want to make any small mistakes and I want to be as prepared as I can be.

I know its a lot of questions but I'd be grateful with whatever people can clear up, specifically on the I.R tests. 


General 
1. Does the banjo bolt at the cu go inside and face out of the cu 
2. does the SY between the DOL and motor only need to be banjo'd at one end as its for interference and not earthing? 


Testing Sheet 
1. would the AM2 bay be best classed as industrial or commercial so I know how long to put the next inspection due in part. 

2. When I measure Ze I know to put the figure down as Zs at DB but on the installation certificate can i put this down too, as its so close to the main incoming supply it would be acceptable. 

Testing 
1. Should I write my water and gas R2 readings on the test sheet or just on the back of the sheet? 

2. I was told we should take all notes on the back of the test sheet but I'm concerned about losing time doing this. 
I know I will be doing the R1+Rn & R1+R2 table for the ring final to write down all figures, and I will write down my RCD trip times, Ze, PFC etc. 
But do I need to calculate my expected R1+R2 figures using the Resistivity of the cable size x cable length and divided by 1000 to comapre them to measured figures? 
I know this will tell me what I should be getting but as I said I'm concerned with losing too much time. 
Also, if my R1+R2 figure at each socket are more than 0.05 ohms +/- would I be expected to fix this or is it fine to leave if it isn't overly high? (I know the spur will be higher) 

3. I'm pretty sure Im ok with this but I just wanted confirmation. After I do my r1, r2 & rn readings for the ring final, if I add togetehr say, r1 and r2 and divide by 4 then that will be my expected R1+R2 reading right? 

4. for the heating system I know I need to do the R1+R2 test up to the FCU to record on the test sheet, but I need to check continuity at all relevant points after the FCU. 
And what would be the best way to do that; wago the cpc and line together in the wiring box/JB and test at each point like normal? 


I.R tests 
I'm worried about not disconnecting all things that are vulnerable to damage when testing. I plan to do the following: 
* disconnect light 
* Replace ring final RCBO with 32A MCB. If 32A MCB is not available is any size ok as its only a low current passing through so for testing purposes it could be even a 6A right? Or would they not accept this. 
* Remove carbon monoxide detector 
* ensure Isolator for TP+N socket is on 

What I'm unure about is: 
* When a FCU/SFCU has a neon, can I just disconect the flyleads and should I just put them in a wago? 
* If the heating circuit is not on a switched spur can I just remove the fuse before testing? 
* I know I need to do the Cu to the DOL and then the DOL to the motor but will leaving the conductrs connected damage the DOL. Should I disconect and wago, and If i do can i not just connect the incoming cables to the outgoing cables of the DOL and not have to do a second I.R test? 
* When doing the lighting, I'm getting confused how many times to operate the switches to cover all combinations. There's a feed to the first two way, then intermediate and then a 2 way and then upto the light, can anybody shed some light into the process of this. 


Any input is appreciated. 


Thanks, 

George

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Ardet R

My thoughts are in red below, these are just my thoughts not the standard answers, stick with what you have been taught in the training if my thoughts conflict.

A key point for the AM2 is to be competent and confident in what you are doing, to have this number of questions may be considered a step backward at this stage.  Try to be confident in what you probably already know.

 

General

Does the banjo bolt at the cu go inside and face out of the cu

Not sure what you want to know here

2. does the SY between the DOL and motor only need to be banjo'd at one end as its for interference and not earthing?

The SY braid from a BS7671 perspective must be earthed as an exposed conductive part (potentially) but may not be used as a cpc, glanding using the SY cable gland at least at one end is required, at both ends is acceptable (so long as there is a cpc in the cable).  The use as a screen is doubtful unless the cable is specifically designed for that use.

 

Testing Sheet

1. would the AM2 bay be best classed as industrial or commercial so I know how long to put the next inspection due in part.

Either way is possible, it would be best to read the titles of the paperwork you will be given in case the type of installation may be mentioned.

 

2. When I measure Ze I know to put the figure down as Zs at DB but on the installation certificate can i put this down too, as its so close to the main incoming supply it would be acceptable.

You do not clarify what you wish to use the Ze figure for expect for the installation certificate, if you wish to use it as the Zs at DB this is acceptable in this case.

 

Testing

1. Should I write my water and gas R2 readings on the test sheet or just on the back of the sheet?

There is not really enough room on the IET standard forms for a value, just tick the boxes and write your test readings on the back of the sheet.

 

2. I was told we should take all notes on the back of the test sheet but I'm concerned about losing time doing this.

You should really have plenty of time and you will need to record the results you measure to demonstrate that you have taken them.

I know I will be doing the R1+Rn & R1+R2 table for the ring final to write down all figures, and I will write down my RCD trip times, Ze, PFC etc.

Ze and PFC can be written directly on the forms, though PSC and PEFC and 2xPSC should be noted on the back.

But do I need to calculate my expected R1+R2 figures using the Resistivity of the cable size x cable length and divided by 1000 to compare them to measured figures?

You should not need to do this calculation, so long as the results you get are of a reasonable level and will provide a compliant circuit then you should be OK.  Have in mind likely limit values.

I know this will tell me what I should be getting but as I said I'm concerned with losing too much time.

Also, if my R1+R2 figure at each socket are more than 0.05 ohms +/- would I be expected to fix this or is it fine to leave if it isn't overly high? (I know the spur will be higher)

Your installation should be compliant to start with so the readings you get will be within the 0.05Ω margin unless you make a measurement error (contact resistance on loose probes for example), you can inform the observer if you are sure the readings are inconsistent, but check for your errors first.

3. I'm pretty sure I’m ok with this but I just wanted confirmation. After I do my r1, r2 & rn readings for the ring final, if I add together say, r1 and r2 and divide by 4 then that will be my expected R1+R2 reading right?

Yes, r1+r2/4 will give you the readings you should get as you measure the resistance at each point of use on the ring during the figure eight test and the highest value measured will be the R1+R2 reading you record and this should be within 0.05Ω of the calculated value, if not a spur.

 

4. for the heating system I know I need to do the R1+R2 test up to the FCU to record on the test sheet, but I need to check continuity at all relevant points after the FCU.

And what would be the best way to do that; wago the cpc and line together in the wiring box/JB and test at each point like normal?

 

After the FCU is not part of the fixed wiring of the circuits it is the central heating control system. 

 

 

I.R tests

I'm worried about not disconnecting all things that are vulnerable to damage when testing. I plan to do the following:

* disconnect light

* Replace ring final RCBO with 32A MCB. If 32A MCB is not available is any size ok as its only a low current passing through so for testing purposes it could be even a 6A right? Or would they not accept this.

Just test the IR of the ring final on the disconnected cables, you should not need to install an MCB. (Unless you have been trained to do this for some reason).  Just do not test the circuit whilst connected to the RCBO.

* Remove carbon monoxide detector

* ensure Isolator for TP+N socket is on

 

What I'm unsure about is:

* When a FCU/SFCU has a neon, can I just disconnect the flyleads and should I just put them in a wago?

Where there is a neon then just wago connect the incoming and outgoing cables bypassing the FCU, or measure up to the switched off FCU and then measure again on the disconnected outgoing cables.

* If the heating circuit is not on a switched spur can I just remove the fuse before testing?

No disconnect the cables removing the fuse will only disconnect the line and not the neutral or cpc.

* I know I need to do the Cu to the DOL and then the DOL to the motor but will leaving the conductors connected damage the DOL. Should I disconnect and wago, and If I do can I not just connect the incoming cables to the outgoing cables of the DOL and not have to do a second I.R test?

The DOL should not suffer from an IR test, but disconnecting the cables  and either doing the two tests or wago connecting past the DOL are both satisfactory methods.

* When doing the lighting, I'm getting confused how many times to operate the switches to cover all combinations. There's a feed to the first two way, then intermediate and then a 2 way and then up to the light, can anybody shed some light into the process of this.

To ensure you have covered all options ideally Measure IR, switch the first switch, measure IR, switch the second switch, measure IR, switch the third switch, measure IR.

On a practical basis measuring when the circuit would be on and changing the state of the first switch to when it would be off and testing at the same point would cover all strappers, remember you only need to test L to E and L to N when switching as the switching does not affect Neutral or CPC.

This diagram showing the live cores when switching may help to clarify the idea, if you think of the red parts of the circuit as being the parts IR tested to other conductors.  You will see that changing the state of one switch will change to the other strapper.

3 wire and 2 wire three way live indications.jpg

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Sharpend

You will find that if you are competent in what you do know and you ask the right questions on what you’re not so sure about then reasonable guidance will be given, a lot of what you are asking is generally covered by the adjudicator asking you questions so you may not necessarily have to write or specifically work out anything providing you show a level of understanding of what you’re being asked. 

The AM2 is not designed to catch you out or trip you up but is merely to establish your work is safe and you have an understanding of what’s and why’s of what you do. You can ask a question to confirm what you believe to be correct, it’s only if you are asking questions that demonstrate you have no understanding that will go against you. 

As for the SY etc you should have available to you all of the correct materials to do all the work correctly. 

A piece of advice is too read and re-read the specification that you are being asked too install, too many people slip up when they mis read the spec and install what they think it said or should be rather than what it actually is. If there is anything specific that the adjudicator wants you to do or note then they will advise accordingly i.e. they will give you the Ze figure as it can’t be truly measured from your bay. 

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