Central Tapped Transformer - wiring

Thread Starter

janger

Joined Nov 27, 2021
10
This is a site-safety transformer. The load connects between the terminals you have labelled "Ve-" and "Ve+", and it gives you 110V AC. When the "Ve+" terminal is at +55V, the "Ve-" terminal is at -55V (and vice-versa 10ms later), so the voltage across them is 110V. (You do not connect the Ve+ and Ve- terminals together. The load does not connect to either neutral or earth)
Its purpose is to limit the voltage on a power tool to 55V AC, which is low enough to prevent a fatal shock in most circumstances.
If the load does not connect either neutral or earth so what do these two yellow terminals represent in the circuit? I thought that there is a +55V in one terminal and -55V in the second terminal which they both go to the load to have a 110V AC power source. If you connect only one terminal you would have 55V in the socket so for example, a hoover would operate on its half power. In 16A 110V switched Internal you have L - terminal N - terminal which in this case is our second L2 - + or - 55V (because there is no neutral ) and Earth terminal. I don't understand why the load doesn't connect to the earth if there is an earth terminal in the internal switch and plug.
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MrChips

Joined Oct 2, 2009
30,712
You don’t connect neutral to earth.
Leave the centre tap not connected to anything.
There is nothing incorrect about this.
What this creates is an isolation transformer. I.e. a floating power supply.
Power hand tools are doubly insulated, for example.
 

Ian0

Joined Aug 7, 2020
9,668
There is nothing incorrect about this.
What this creates is an isolation transformer. I.e. a floating power supply.
Power hand tools are doubly insulated, for example.
Judging by the wiring colours this is British or European, in which case the centre tap must be earthed.
Looking at the transformer connections, I expect the transformer manufacturer has already connected the centre-tap to the earth screw.
The output will be on this type of socket which has an earth terminal.
Not all hand held power tools are Class II, there are plenty that are Class I and have an earth connection.
 

Thread Starter

janger

Joined Nov 27, 2021
10
@Ian0 @ericgibbs I did the final diagram.
Ian0 - I understand. There is no Neutral instead of it we have L1 and L2. Earth from the 110V outlet goes to CTE- Center Tapped Earth which is connected to the transformer earth terminal
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