Control Transformer: Voltage to Ground

[Dale Hayes]

The following questions relate to a 380V to 220V, 250VA, 1ph, Control Transformer.

The transformer is fused on both connections on the primary side and at both X1 and X2 connections on the secondary side.

Based upon NEC 250.21(A, 3 a. & b.) the transformer will not be grounded at X2.

Questions:
1. On the 220V secondary, what is the voltage from X1 to X2.

2. On the 220V secondary, what is the voltage if a reading is taken from X1 to ground. (As stated earlier the transformer is not grounded at X2)

3. On the 220V secondary, what is the voltage if a reading is taken from X2 to ground. (As stated earlier the transformer is not grounded at X2)

 

[don_resqcapt19]

The following questions relate to a 380V to 220V, 250VA, 1ph, Control Transformer.

The transformer is fused on both connections on the primary side and at both X1 and X2 connections on the secondary side.

Based upon NEC 250.21(A, 3 a. & b.) the transformer will not be grounded at X2.

Questions:
1. On the 220V secondary, what is the voltage from X1 to X2.

220 volts.

2. On the 220V secondary, what is the voltage if a reading is taken from X1 to ground. (As stated earlier the transformer is not grounded at X2)

Anything from 0 to 220 volts.

3. On the 220V secondary, what is the voltage if a reading is taken from X2 to ground. (As stated earlier the transformer is not grounded at X2)

Anything from 0 to 220 volts

If the voltage readings in Q2 and 3 are taken at the same time, they will total 220 volts.

 

[Dale Hayes]

The 380V to 220V Control Transformer is fused on both the primary and secondary connections. The Transformer is not grounded on the secondary
X2 connection.

On the 220V secondary is both X1 and X2 "hot", the same way that 240/120, 1-phase household current is 240V line to line, and 120V line to neutral?


Can the 220V transformer secondary be grounded at X2?

 

[brian john]

The 380V to 220V Control Transformer is fused on both the primary and secondary connections. The Transformer is not grounded on the secondary
X2 connection.

On the 220V secondary is both X1 and X2 "hot", the same way that 240/120, 1-phase household current is 240V line to line, and 120V line to neutral?

X1 is "hot" to X2, to ground the voltage as noted can be anything from 0-220

Can the 220V transformer secondary be grounded at X2?

Sure or at X1 the ground (earth, and any metallic current carrying components of the system) do not care. Grounding will simplify trouble shooting.

 

[Smart $]

The 380V to 220V Control Transformer is fused on both the primary and secondary connections. The Transformer is not grounded on the secondary
X2 connection.

On the 220V secondary is both X1 and X2 "hot", the same way that 240/120, 1-phase household current is 240V line to line, and 120V line to neutral?


Can the 220V transformer secondary be grounded at X2?

You imply by virtue of omission there are no other connections on the secondary. Is this correct? If not, what other connections are there and are any grounded?

So far, all the answers the others have provided are based upon there only being the two secondary connections, X1 and X2.

 

[Dale Hayes]

We have local panel builders that do not ground X2 if the voltage is 220V. They connect a red wire to X1, and a black wire to X2. They fuse both X1 and X2 and they break both lines X1 and X2 with the control Off-On operator. Seems like they treat X1 and X2 as "Hot" wires.

My question - can I wire the 220V secondary like I would a 120V secondary with a red wire to X1, a white (neutral) wire to X2 and a green (ground) wire to X2?

 

[don_resqcapt19]

...
My question - can I wire the 220V secondary like I would a 120V secondary with a red wire to X1, a white (neutral) wire to X2 and a green (ground) wire to X2?

Yes, you are permitted to ground that system. Once you do, you do install it just like any other grounded system.