Do TN-S Systems Need PEN Protection?

⚡ What is a broken PEN ⚡

Safety is key in the electrical industry, especially when it comes to earthing arrangements like TN-C-S (Terra Neutral Combined Separate) and TN-S (Terra Neutral Separate) systems. In this video, we break down the differences between these systems, their pros and cons, and why DNO networks are shifting from TN-S to TN-C-S due to aging underground cables.

What you’ll learn:
Why the transition from TN-S to TN-C-S is happening
The risks of TN-C-S systems and the importance of open PEN protection
How proper feeder pillars ensure safe earthing
Essential protective measures for EV charger installations

This series of videos is supported by Lewden Pallazoli

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Time Stamps ⏱
00:00 TN-S Systems and PEN Protection Explained
00:21 Understanding TN-C-S Systems
01:13 Overview of TN-S Systems
01:35 The Concept of a Broken PEN
03:17 PEN Protection Requirements for TN-S Systems
03:52 How Suppliers Convert Incoming Feeds to TN-C-S
05:00 Time to Validate Your Learning
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#ElectricalSafety #EarthingSystems #EVChargers

[in]

Generally TN-S mains cables are repaired or altered with 4 core cable, but unfortunately, as the video shows, too many DNOs have altered 4 core mains/PILC mains TN-S) cables by jointing in 3 core (TN-C-S) cables. So therefore customers’ supplies cannot be considered TN-S just by seeing split concentric or PILC at the cutout. Unless your supply is a direct service cable between the sub-station/pole mounted transformer and the cutout and known to be split concentric/4 core, no DNO can confirm your supply is true TN-S. This has been a problem since the introduction of CONSAC/3core mains cables by DNOs since the early ‘70s.

[darrenowen]

Please get rid of the sound effects - they are very annoying on an otherwise excellent video. Thanks.

[_Miner]

Had a broken pen this morning so had to use my pencil. A right start to the day.

[sambrown]

Please keep the sound effects, they kept my brain engaged 🙌🏽

[andysims]

My old Boss would only recognise TT systems on new builds and rewires . . Every new job or rewire we done he made us fit an earth spike and additional
RCDs . He would never trust using the supply company’s Earth .

[WolfGamerBohumin]

This is the reason why Czech standards require PEN split point and MET to be grounded on site.

[sadken-grve]

As the loss of the supply neutral seems to be such a big issue now it begs the question why PEN fault protection isn't mandatory for installations in general?

[petertallowin]

I find this interesting. I had a charger install on a looped TN-S system a while back. Client contacted DNO as I instructed and they permitted the connection of the charger and arranged a date to un-loop the supply. I was convinced that when UKPN came to carry out the works that they would convert the system to TN-C-S but they left it as TN-S. Looks like I will be returning to retrofit the Garo unit. My question is this. If we are to now assume or treat TN-S as TN-C-S. What happens when the Ze is above 0.35? Which it frequently is on a TN-S.... Carry on reporting high Ze? I have also had clients do this to be told it's fine, it's not that high...

[tdlcraig]

On another note, this is why i always fit a plastic coupler on any copper piping before taking it to an outside tap.

[johnschlesinger]

My supply is TN-C-S, via OHL. I have had three electrodes installed for extra safety. Your diagram shows multiple electrodes on the PEN, but the PME approval only requires one extra electrode in addition to the electrode at the transformer. The OHLs round here all have electrodes on the poles, usually every three poles.

[yngndrw.]

Do those feeder pillars come in a version which can take the supply cutout and meter? I couldn't find a version with extra space for that.

[sergiofernandez]

Safest way for your average dwelling is Open protection IS needed. The counter argument is cost as some Electrician will quote a cheeper unit with lacks PEN protection. This also has included national installers. The regs need to make OPEN mandatory.

[RJSElectricalCheshire]

Yes, they do unless you can guarantee that it's a true TN-S and will not be converted into a PME in the future.

[MrTillychicken]

Yes, this fault is a real danger to life and with an aging network only going to get more prevalent. Our college lecturer made us aware of this over 30 years ago when we were fitting main earth blocks with moveable links for testing! Not in any regs book but was told to check for a PD/back feeds when removing the link between the supply CCP and main bonding. To much time now goes on theoretical risks and not tackling the supply companies, NIC EIC and the likes should be lobbying government.

[andysims]

Why on that picture you show are the main tails and earth going through separate grommets to the DB . Is it plastic, if it’s metal what about Eddy currents

[stevenhargreaves]

If everything in property 2 and 3 is still working as you said in the video and voltage is still at 230VAC between L-N then it will also be 230VAC between L-E as they are connected at the MET. The circuit is complete by all the parallel paths through everything connected to earth and even go back to the neighbouring property, property number 1s neutral that is still connected.

My understanding is that the voltage between earth and true earth becomes 230VAC or increases more when property 2 and 3 is "not working", effectively the impedance is higher between load-electrode (electrode been all the parallel paths back through the MET) than source-load which means that most of the voltage is between the load-electrode, (in simple terms).

So wouldn't the potential difference between earth and true earth be the same before and after the open pen fault if property 2 and 3 are functioning normal with same voltage between L-N and L-E?

How does the open pen detector detect the 1st scenario if the voltage in property 2 and 3 is still stable. Is it monitoring the impedances and sees a change, although even without a neutral conductor back you can still have a very good path back to the transformer through all the things connected to MET and therefore through neighbouring properties, as you described in the video.

[DH-tvyw]

Pretty sure we had one of these faults in our street around a year ago after an initial powercut. Neons glowed dimly and motors whined as they ran slowly. Fridge freezer packed up a week or two later. Pretty sure that this was a PEN fault.

[ChariotsofWire]

The only PEN issue which needs sorting, is the one the DNO use to write off responsibility for their shite. About time they took ownership of their ancient junk.

[ShaWoddyWoddy-xi]

TNCS the neutral is the earth so lose neutral and lose earth so everything is live.
TNS you have a separate earth

[rossdrummond]

Yes, otherwise the ink leaks in your pocket🖋