Confused about isolation transformers

Thread Starter

Si6685

Joined Jul 20, 2019
12
Hi. I’m new to training in plumbing and am studying electrical as well in an aim to have a well rounded knowledge. I have a relatively good understanding of basic electricity and circuits, I understand earth reference transformers but am still slightly confused about isolation transformers.

Say I have an isolation transformer with the same primary windings as secondary and producing 230Vac which is what is used here in England. Now my confusion lies here. Now isolation transformers have no earth reference and the two conductor wires are now said to be floating, I understand that but am still confused on what the voltage is doing. Are both wires now hot and could have any voltage on them? Does +230 volts go through one hot while the other is -230 and then they switch on each part of cycle? I’ve also read people say the voltage is half on each leg.

I’ve googled I’ve read forums and even asked elsewhere but have yet to have a definitive answer.

I’m hoping someone here can clear this up for me.
 

MaxHeadRoom

Joined Jul 18, 2013
19,387
In N.A. and I believe also in the UK, you can re-reference one side of the secondary to the earth ground point/conductor, this terminal is then used for the neutral conductor, and treated as such.
I have a N.A. NFPA79 picture of the circuit I will dig out and post.
Max.
 

Thread Starter

Si6685

Joined Jul 20, 2019
12
Thanks. Yes looking at this it’s similar to how things are done over here. However my question is aimed at isolation transformers, those without an earth reference and just two conductor wires.
 

MaxHeadRoom

Joined Jul 18, 2013
19,387
Thanks. Yes looking at this it’s similar to how things are done over here. However my question is aimed at isolation transformers, those without an earth reference and just two conductor wires.
The appliance connected to the secondary of the transformer sees exactly the same conditions as the earth grounded version, it is still 230vac whether grounded or not.
Ground is just a reference point and has no effect on the voltage supply itself
Max.
 

Thread Starter

Si6685

Joined Jul 20, 2019
12
Thanks Max. Yes I have seen this video. John Ward is actually someone who’s videos I study a lot and has taught me a lot. This video is to do with centre tap building transformers as you mentioned.
 

MaxHeadRoom

Joined Jul 18, 2013
19,387
The bottom line is that your isolated 1:1 secondary is exactly the same as the primary side, as far as the secondary load is concerned, it will not tell the difference as there is virtually non.!;)
Max..
 

Thread Starter

Si6685

Joined Jul 20, 2019
12
The appliance connected to the secondary of the transformer sees exactly the same conditions as the earth grounded version, it is still 230vac whether grounded or not.
Ground is just a reference point and has no effect on the voltage supply itself
Max.
You may have just answered my question then. So during +230 volts the electrons move towards the higher potential and during the negative part of cycle the electrons flow the opposite.
I was getting confused because some places I read both were hot wires etc
 

nsaspook

Joined Aug 27, 2009
6,572
First you need to define what does 'HOT' mean from a reference point. With a floating secondary all secondary wires are 'hot' with each other.
You may have just answered my question then. So during +230 volts the electrons move towards the higher potential and during the negative part of cycle the electrons flow the opposite.
I was getting confused because some places I read both were hot wires etc
One simple trick to stop confusing yourself. Stop thinking about electrons.
 

MaxHeadRoom

Joined Jul 18, 2013
19,387
HOT is usually used as a reference to earth GND. If not grounded, they become both Hot in name or description.
But as far as current flow etc, nothing has changed.
Max.
 
To measure any voltage, you need a reference.

An isolated transformer has NO reference.

So, you have to use two points on the secondary side.

"isolation transformers" in electrical circuits generally create a control voltage. e.g. so a switch doesn't have to operate at 480 V.

"Isolation transformers" with a grounded secondary have better ground characteristics.

In the US anyway, we have 208 and 240 three phase supplies in an industrial setting. A 240 to 120 transformer creates the control voltage of 120 VAC.
 

MaxHeadRoom

Joined Jul 18, 2013
19,387
Thanks NSA, Max and Keep it simple! Like I said I’m still at a very basic level but you cleared it up for me
I originally started out in the UK with a Industrial Electricians license, but have been away far too long to be aware of many of the current rules on isolation and grounding there, even the wire sizes have gone metric, AFAIK!:p
Max.
 

MrChips

Joined Oct 2, 2009
19,727
One thing to note is that voltage is always a difference in potential.
It is measured between two points A and B.

As I usually point out, it is like measuring distance.
It is meaningless to ask, "What is the distance at Manchester?"
A more meaningful question would be, "What is the distance from London to Manchester?"

If the secondary of your isolation transformer is not referenced to any absolute voltage, it is "floating". That is, the terminals A and B are +230 x 1.4 V apart at the peak of half the cycle and -230V x 1.4V at the other half, i.e. the sine wave amplitude is actually 230 x √2 = 325V. (That has to do with something called RMS which I can explain later.)

Point A could be 1325V while B is 1000V or any voltage offset you choose. The secondary could still be floating.
 

MaxHeadRoom

Joined Jul 18, 2013
19,387
Hi. I’m new to training in plumbing and am studying electrical .
On an related note. just to get an an idea as to when I started, the plumbers had to know and be skilled at wiping a lead pipe joint, one of them gave me a lesson on how to do it, they could do it so it looked like it had been turned on a lathe!
Probably a skill not needed any more?
Max.
 

Thread Starter

Si6685

Joined Jul 20, 2019
12
Thanks MrChips. Like I said I’m just trying to further my knowledge to have a well rounded understanding. The majority of my training and knowledge lies with oil fired appliances ie. pressure jet burners and vaporising burners but it can’t hurt to know electricity to extent. Obviously any electrical work is carried out by a qualified electrician but I’m keen to learn
 

Thread Starter

Si6685

Joined Jul 20, 2019
12
You tend to have specialist lead workers over here now Max. Basics is taught during college to plumbing students but again it’s usually lead specialist firms who do the work.
 
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