§ 10 Schemes for connecting meters.
Counters are connected to the network in two ways: directly into the network (direct-connected meters) and through current and voltage transformers.
Fig. 1 Connection diagram for a single-phase meter.
Fig. 2 Scheme of direct connection of CP4-I679 type meters with rated currents of 20 A or more into a three-wire and four-wire network.
Fig. 3 Scheme of direct connection of CP4-I678 type meters with rated currents of 20 A or more in a three-wire and four-wire network.
Fig. 4 Scheme of direct connection of meters of type SA3-I677 with rated currents of 20 A or more into a three-wire network.
Fig. 5 Connection diagram of meters СР4У-И673М and СР4У-И679 with rated currents 1, 5A through any current transformers into a four-wire and three-wire network.
Fig. 6 Connection diagram of meters СР4У-И673М and СР4У-И679 with rated currents 1, 5A through any current and voltage transformers into a three-wire network.
It should be noted that induction meters spin their drive most quickly when connected correctly. Counters (especially when using current and voltage transformers) have much more reasons to spin slower than they should:
- Current transformers may be confused (instead of 3 pcs. 300/5 costs 2 pcs. 300/5 and one 600/5). However, a transformer with a lower coefficient can be supplied, and then the counter will spin faster (although in this case the likelihood that this current transformer burns from overload increases) and it is very easy to mix it up - especially on old plates so slurred that even on a removed transformer under a lamp and a magnifying glass do not always make out what is written on them. And in an electric panel, somewhere below, it is completely impossible to make out. We have to drag a whole bunch of devices.
- The beginning and end of one of the current transformers may be confused, then 2 phases will wind forward and one phase backward (although in the end the counter will wind forward, although less than expected)
- The phases on the counter may be reversed. That is, a current transformer from phase A is connected to the counter at input 1, and the voltage comes from phase B. Usually this is easily detected - the counter winds back.
- Non-contact or breakage of one of the current transformers is possible. Then the load of one of the phases will not be taken into account.
And if you get a little distracted, then sorting out a pile of wires, especially when there are 3-4 counters on the panel, is not always easy even for an experienced electrician-relay operator. In this sense, electronic ones are good in that if something is connected incorrectly, they immediately swear (that is, they give an error message), but they are still expensive even for industrial enterprises.