What do the line-and-circle symbols mean on these electric meters?

Question

I was looking at an electrical installation and came across unfamiliar symbols on the front of a pair of meters.

These are from three-phase 240v meters running on a timed system. One each for peak/off-peak usage.

On the first image, I recognise part of the lower row: indicating 50Hz frequency, Unknown symbol Double insulated CE safety mark

I don't however recognise the line-and-circle symbols nor the ratchet-type symbol. I have been unable to find search terms to even start looking them up?

My best guess is that it has something to do with supported wiring schemes for the meters.

Can anyone shed some light as to what these are called and what they mean?

Thank you.

Is it power meter? Probably means the mechanism can not go in reverse. — user263983, Apr 09 '21 at 11:17
Hmmm The cog and wedge symbol I would assume means the meter is non reversible so you can't roll it back. The line and dot diagrams from the bottom white diagram in order look like 3 phase, single phase, single phase line to line, two phases of 3 phase, and the V and L shaped I'm not sure of. A 90 degree angle may indicate true vs reactive or something, but the 60 degree angle... hmmm. — K H, Apr 09 '21 at 11:49

Theodore · Accepted Answer · 2021-04-09T19:30:10.710

35

Below are my interpretations of the various symbols. I included more than just the line-and-circle symbols, for the benefit of future visitors:

50 Hz AC:

Double Insulated:

Non-reversing (not suitable for power export or net-metering):

CE Marking (meets European Community standards):

Three-phase Wye:

Single-phase plus grounded neutral:

Single-phase ungrounded:

Single phase with center tap neutral:

Two phases of 3-phase system, plus neutral (This would give you 230V from phase to neutral, or 400V between phases, but no three-phase):

Corner-grounded 3-phase open delta:

Quadrature (phases 90° apart):

Contains lithium battery (probably for backup or to power a communications device):

edited Apr 09 '21 at 19:30

answered Apr 09 '21 at 14:20

Theodore

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11
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Instead of "Single Phase Ungrounded" could you say "Single Phase Line to Line"? The system should still be bonded and grounded, even if no neutral is present or system is isolated. Nice answer. – K H Apr 09 '21 at 21:59
1

@KH It's entirely possible for it to be ungrounded - not everything is a residential service. Isolated systems exist, usually in situations where continued service through a fault is desired. It could just be a single-phase without the meter seeing a neutral, but the meter doesn't care whether it's grounded or not. – SomeoneSomewhereSupportsMonica Apr 10 '21 at 03:23
@SomeoneSomewhereSupportsMonica Non current carrying parts are usually bonded, grounded or isolated, and an isolated system where they didn't bond and ground the non current carrying parts would be rare. There was a question recently about a shipboard system for example that used isolated 480V delta with ground fault detection. If the system is not bonded and grounded, ground fault detection does not work in that case. Even without a grounded neutral/identified conductor, saying "ungrounded" is a misnomer and untrue, and "line to line" more clear. – K H Apr 10 '21 at 03:39
Who is Monica? Is there some sort of ancient grass roots political movement going on around here? – K H Apr 10 '21 at 03:41
Monica was sorely mistreated by SX. – Jasen Слава Україні Apr 10 '21 at 04:20
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@KH Here's a thread that describes the events of late 2019 relating to Monica Cellio, which prompted a lot of users to add messages supportive of her to their display names: https://meta.stackexchange.com/questions/334399/summing-up-the-main-issues-the-story-so-far – Cassie Swett Apr 10 '21 at 06:51
@KH It's also common (although less so now that RCDs/GFCIs are available) for small parts of installations to be protected by isolating transformers. It would be very rare for those to be separately metered by revenue-grade meters, though. – SomeoneSomewhereSupportsMonica Apr 10 '21 at 08:28
@SomeoneSomewhereSupportsMonica Yeah it's not impossible. Old wood frame housing installs with just GFCI protection and no safety ground for example. The point remains though that he has said "Single phase ungrounded" where while there is no neutral present, there may be grounding. Saying Single phase Line to Line is more accurate regardless of whether a ground is present. There are other bits of confusion it can avoid too since the meter could be installed in this configuration on a line to line load of a 3 phase wye system with both ground and neutral available. – K H Apr 10 '21 at 08:45
@KH: A floating 480V system could alternately connect each leg to ground through a high resistance or other current-limiting means, and measure the voltage on that leg. This would simultaneously increase the number of single-point failures that could be detected, and reduce the number that would be immediately dangerous if the system wasn't shut down. In e.g. a US system with anti-phase 120V hots, if an oven's heating element developed a short to ground somewhat near its midpoint, that might cause one half of the element to get much hotter than the other... – supercat Apr 10 '21 at 21:04
...but unless there were a GFCI no fault would be detected. On a floating system with ground sensing, however, whichever leg had the shorter resistance path to ground would have at least 120 volts AC on it even when connected to ground through a 100K resistor [neither leg should should show any voltage in the absence of leakage, so the presence of 120V would indicate a clear fault, even though peak ground current would be less than 5mA. – supercat Apr 10 '21 at 21:09
@KH I am using "ungrounded" as it is used in US/NEC to indicate that none of the current carrying conductors are bonded to earth ground. It is allowed under certain circumstances. (Which may not be how it's used elsewhere. I recognize that this is clearly not a piece of equipment intended for use in the US.) FWIW, I have seen 4160V 3-phase, utility services that are truly ungrounded. (They served municipal water wells) There were 480V and 208V systems derived from these that were Wye (star) grounded. – Theodore May 07 '21 at 21:57

score 17 · Answer 2 · answered Apr 09 '21 at 12:37

In order of appearance:

Three-phase star (wye) connection.
Two-phase and neutral. (Note that if neutral isn't present then it would be a single-phase connection.)
Quadrature (90°) phases and neutral.
Split phase (180°) and neutral.
Single phase and neutral.

The ratchet symbol indicates that the meter won't run backwards and so won't register exported energy. This is common because there would be a different tariff for consumption and supply. Import and export could be monitored by connecting two of these meters back to back.

What do the line-and-circle symbols mean on these electric meters?

2 Answers2