Grounding 24 volt transformer

[Cisco007]

Hey guys
I’ve got a 120volts to 24volts transformer ..I need to ground the secondary 24 volts side, but there’s no indication on the transformer or from the manufacturer on which one of the two wires coming out of the secondary side of the 24 volts to ground ..which one of the two wires do i ground on the 24 volt side of the transformer..?

Thanks

[kdean1]

Take your pick. The 24V side is the opposite of the common side.

There have been some posts here about phase(?) on the transformer and relationship to neutral on the line voltage side but I have not encountered a situation that required switching them. Perhaps someone will comment who has experienced it.

[Cisco007]

What do you mean by take your pick...any of the two wires coming of the the secondary side i could ground?

Thanks

[kdean1]

yes. Whichever you pick to ground, the other side will be 24V. The 24V side is the one that gets switched, common should be uninterrupted.

[Cisco007]

Thanks ..

[kdean1]

You're welcome. I hope it solves the issue for you.

[CHAINIK]

Take your pick. The 24V side is the opposite of the common side.

There have been some posts here about phase(?) on the transformer and relationship to neutral on the line voltage side but I have not encountered a situation that required switching them. Perhaps someone will comment who has experienced it.

Thats a possibility with systems where there are two transformers wired in parallel. Two 24v xfmrs with the secondaries wired in parallel will give 24 volts at the secondary. If they are wired out of phase, the secondary voltages will sum to 48 volts. Similar to measuring from hot to neutral at the panel vs hot to hot.

[ch4man]

polarity= L1 to ground, 120V. neutral to ground, 0 volts
ground/bonding= ground (EGC) to chassis, 0 volts
phasing a transformer= L1 to R, 96 volts. Out of phase= L1 to R= 144 volts.
correct phase= primary voltage minus secondary voltage, out of phase, voltages add together.

for what is worth.......

[stumpdigger]

Hey guys
I’ve got a 120volts to 24volts transformer ..I need to ground the secondary 24 volts side, but there’s no indication on the transformer or from the manufacturer on which one of the two wires coming out of the secondary side of the 24 volts to ground ..which one of the two wires do i ground on the 24 volt side of the transformer..?

Thanks

The only transformers that were grounded on the secondary side I had to replace because some electrician thought everything needs to be grounded! Don't ground low voltage secondaries! Why would you want to ground L1 or L2?? You do not ground live wires. if the secondary goes to ground it is screwed down to grounded metal. You are confused about the American 120 VAC system that uses a neutral instead of just using 240 VAC system like Europe. We use 120 VAC because A. Edison was in a war with Tesla about electrical distribution. Edison lost because he was completely wrong and wanted to use DC. We run 765,000 VAC in transmission lines to lower amperage and wire size then just drop VAC as necessary thru transformers. Most people die of electrocution from a 120 VAC circuit that has lost a path to ground (neutral).

[ehsx]

The only transformers that were grounded on the secondary side I had to replace because some electrician thought everything needs to be grounded! Don't ground low voltage secondaries! Why would you want to ground L1 or L2?? You do not ground live wires. if the secondary goes to ground it is screwed down to grounded metal. You are confused about the American 120 VAC system that uses a neutral instead of just using 240 VAC system like Europe. We use 120 VAC because A. Edison was in a war with Tesla about electrical distribution. Edison lost because he was completely wrong and wanted to use DC. We run 765,000 VAC in transmission lines to lower amperage and wire size then just drop VAC as necessary thru transformers. Most people die of electrocution from a 120 VAC circuit that has lost a path to ground (neutral).

???????????
Wire per the vendor diagrams. I have had gas valve open with no safeties because of loose or disconnected 24vt grounds, solid state controls intermittently not function and other fail because of inadequate grounding.

[stumpdigger]

???????????
Wire per the vendor diagrams. I have had gas valve open with no safeties because of loose or disconnected 24vt grounds, solid state controls intermittently not function and other fail because of inadequate grounding.

Wondering if I understand. Are you saying a poor chassis ground on a 24 VAC causes your circuits not to funtion properly? Are you sending current through the chassis? Never saw that, circuit boards always worked just fine for me.

[BBeerme]

If this transformer is going on a unit that has heating with flame rectification to sense the flame, polarity of the transformer and which side gets grounded is critical.

So you always fire off the heating to be sure you don't/won't have a call when it gets cold.

[BALloyd]

Wondering if I understand. Are you saying a poor chassis ground on a 24 VAC causes your circuits not to funtion properly? Are you sending current through the chassis? Never saw that, circuit boards always worked just fine for me.

In the United States, for example:

◆The National Electrical Code® requires (section 250.20) grounding transformers for AC systems of less than 50 volts if the primary voltage exceeds 150 volts to ground or if the main transformer supplying power to the building is ungrounded.

◆Some municipal electrical codes more restrictive than the NEC may require that the secondaries of all transformers that supply 24 VAC be grounded

[ehsx]

Wondering if I understand. Are you saying a poor chassis ground on a 24 VAC causes your circuits not to funtion properly? Are you sending current through the chassis? Never saw that, circuit boards always worked just fine for me.

The 24vt is ac, without grounding it can back feed to grnd and cause, in the case I had the gas valve to energize on a call for heat, bypassing ignition and safeties, old Trane rooftop. The gas valve was the last component in line and had enough voltage to open the valve. Found the xformer grnd hanging behind a relay unconnected. A good way to blow up a building, I could smell gas when I drove up into the parking lot.

On a number of units with solid state furnace controls and old 2 wire electrical service had to add equipment grounds and would add a surge suppressor for good measure also. Electronic t'stats without ground wires would also cause problems with electronics down stream that did not have ground terminals, same with two wire time delays and electronic controls downstream, intermittent malfunctions.

On a chiller the mfg tied the 24 vac and 24 vdc commons together on a controller causing intermittent issues and controller failures. Had to grnd the 24 vac separately.

[Tom27]

Doesn't the current NEC call for the secondary to be grounded?

[ehsx]

Yes, in most all cases.
NEC "Circuits under 50V may have to be grounded. (sec. 250-5)". "If supply system operates ungrounded, then secondary must be operated grounded regardless of voltage."

Wiring by mfg has to be certified by an "approved agency" UL, ETL, CUL....

[stumpdigger]

If this transformer is going on a unit that has heating with flame rectification to sense the flame, polarity of the transformer and which side gets grounded is critical.

So you always fire off the heating to be sure you don't/won't have a call when it gets cold.

The solid state flame rectifier uses a simple electronic current relay, when it senses current flow from the flame rod to anywhere it proves pilot. If you deliberately ground out the flame rod the relay circuit senses a failure and opens. Clean the rod and pilot hood

[stumpdigger]

In the United States, for example:

◆The National Electrical Code® requires (section 250.20) grounding transformers for AC systems of less than 50 volts if the primary voltage exceeds 150 volts to ground or if the main transformer supplying power to the building is ungrounded.

◆Some municipal electrical codes more restrictive than the NEC may require that the secondaries of all transformers that supply 24 VAC be grounded

They are speaking of an extra ground on the transformer which is taken care of as it's screwed to the chassis.

[stumpdigger]

Doesn't the current NEC call for the secondary to be grounded?

Special for you , it's grounded at the chassis.

[stumpdigger]

The 24vt is ac, without grounding it can back feed to grnd and cause, in the case I had the gas valve to energize on a call for heat, bypassing ignition and safeties, old Trane rooftop. The gas valve was the last component in line and had enough voltage to open the valve. Found the xformer grnd hanging behind a relay unconnected. A good way to blow up a building, I could smell gas when I drove up into the parking lot.

On a number of units with solid state furnace controls and old 2 wire electrical service had to add equipment grounds and would add a surge suppressor for good measure also. Electronic t'stats without ground wires would also cause problems with electronics down stream that did not have ground terminals, same with two wire time delays and electronic controls downstream, intermittent malfunctions.

On a chiller the mfg tied the 24 vac and 24 vdc commons together on a controller causing intermittent issues and controller failures. Had to grnd the 24 vac separately.

The transformer comes with two posts, two conductors out of phase at +/- 24 VAC sixty cycles/ second; 60Hz if you prefer. There is no ground, there is no neutral, it's just two hot legs. L1 (red) and L2 (common). If you are having issues with grounded 24 VAC systems it is because you are grounding HOT and/ or COMMON. If some engineer wants to ground some circuit board ect. ,they will do it by means of mounting screws. And please do not mix A/C and D/C CIRCUITS.