It is a piece of brass sweated to a piece of copper.
new meter has no off-switch
- Thread starter karaman
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Yes
Yes, there aren't many on the system but those that I have seen are like this, similarly when we used to install isolators they, despite being DP only switched the live.
The original idea was for these systems to be installed on new supplies, we could energise the supply and leave it for the electrician to connect up!
As we know subsequently the idea was dropped (no idea why) so they don't get fitted any more.
I would suggest that the small device on the bus-bar in the meter is a small CT.
Hmmm. In terms of the language I speak, I'm not sure how that would qualify as "DP" ("DP isolator").
As I said, that's what I would have expected to see, but it's now been confirmed that, just like it looks, it's just a lump of brass! I have to say I'm surprised - but if I suppsoe that if they are getting a voltage drop method to work satisfactorily, then it's probably a fair bit cheaper than it would be with a transformer, even when one takes calibration process into account.
Kind Regards, John.
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Wontdothatagain: It would be instructive to know what the 2 ICs say on them, if you still have that meter open.
The isolator was DP but only the Live was connected to it, the Neutral was in a Henley block
I had to open another non isolating meter as i could not see the info on the other one but apart from the layout they look the same,
Small IC 272C 077 CTJ7
Large IC 51961600 M38503M2H312FP 038A101
On this meter there is an extra IC CSI 42 24C042J 0010A
K
kai
It shows that certain DNO fitters do not know what they are doing! _ Why spend more money on a henley block, when the Isolator could have been properly wired up in the first place!
Quite. Even if (as seems to be the case) DNOs and the regs they work to do not require DP isolation, I certainly can't think of any harm that can result from DP isolation - so, as you say, to do what has been described is simply a waste of money!!It shows that certain DNO fitters do not know what they are doing! _ Why spend more money on a henley block, when the Isolator could have been properly wired up in the first place!
Kind Regards, John
I think part of the thinking with the DP isolator is that if there is off-peak in use this would use the "other" pole.
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Wontdothatagain: Thanks for that. It makes sense - a dual op-amp, processor and serial eeprom. I guess the first version had EEPROM built into the processor.
It shows that certain DNO fitters do not know what they are doing! _ Why spend more money on a henley block, when the Isolator could have been properly wired up in the first place!
In my area, SSE & WPD, they stipulate that the Neutral must NOT be switched before the customers instalation. WPD tend to use Henley blocks but SSE use a new version of the Wylex REC2 & REC4 where the neutral terminal is a solid link but still part of the switch.
Errrrrrr, Yes, what he said above.
Seriously, can you expand on it. I fit the damm things and can undestand how a CT meter works fine but this is the first time that i have gone into a single phase meter trying to understand how it measures the current. I know that many poly phase meters have small CT's around an extension post ontop of the cable terminal and they measure that way.
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OK I was talking in general terms only. The EEPROM (a memory chip which stores data even when the power is off) is needed to store the meter readings and also the calibration information.
The processor looks at the incoming values of current and voltage. It presumably does this many times during each mains cycle so that it can calculate the true power used, as opposed to the volt-amps. I understand that domestic users in the UK pay for true power used. So the processor needs to integrate the volts*amps product.
The voltage is obtained from a resistive potential divider tapping the mains voltage between L and N. The current seems to be measured by allowing a small voltage drop across a very low resistance (the piece of brass?) and using an operational amplifier to amplify this. The processor presumably has analog to digital input converters to take the amplifier voltages and turn them into digital values.
A mystery to be at the moment is how the negative voltages are kept within range, but I expect there is an easy answer. It would seem to be unfair to the consumer to assume that the negative excursions are using the same current as the positive ones.
Calibration woud be an automated process taking a few seconds, and would be required in any case for a consumer meter.
This is all guesswork.
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