Identifying cables from proxy to plc

[Shaun12]

Looking inside a panel i noticed the 0v and 24v from a sensor went to a row of terminals before the I/O. They were labelled up h1 24v (brown) and a h2 0v (blue). I was just wondering why h1/h2 instead of 24/0v? Is this simply just how the designer chose to identify them or does the h mean something else?

 

[Bobster]

Could mean anything.

Is there a site standard noclamenture?

In control systems I design wire numbers correlate to the page they originate on in the drawing set. For instance wire 101 would be sheet 1 wire 01.

 

[snowhead]

Are there other PLCs in the same system, maybe there's and A,B,C etc?

 

[Shaun12]

I thought that as well but looking in another panel the remote i/o has the same id (h1/h2)

 

[netblindpaul]

They could all be common, i.e. 24V d.c +ve & the -ve of the 24V d.c. supply, with the signal wire from the poxy proxy being differently numbered?
Or, the machine builder could be a numpty who does not know how to build panels!

 

[Shaun12]

Yeah the signal wire is labelled with the input address.

 

[netblindpaul]

So, they are not actually different wires then are they, they all are the same +24V d.c./-ve or 0V of the d.c. supply.
One cannot label each individual wire which is connected to the same common voltage source with a different identification, else how would you know that they are connected to the same voltage source.
This is standard and perfectly acceptable practice under EN60204 & the machinery directive.

 

[Shaun12]

I didn't say they were different wires. They are all from the same supply, like you said. I was just wondering why H1 and H2 were used as the cable i.d (those specific letters and no.s)

 

[Shaun12]

Is it just random? Could be xyz 1 and 2..

 

[netblindpaul]

Ahh right.
This could be down to contractural requirements, company stadards, seller or buyer?
The designator H in EN 81346 does not relate to a power supply, not a proximity switch.
It could however, relate to the function of the machine itself perhaps.

 

[Stu1312]

I imagine it's wired in accordance with the BEBS 12 standard for small panel wiring. This gives the standard suffixes for panel wiring identification. It's been superseded now (can't remember what the new standard is called) but the identification suffixes are still the same I believe.

 

[netblindpaul]

However, BEBS 12 is not a harmonised standard under the machinery directive.
The harmonised standard for machinery under the MD is EN 60204-1.
I would expect that it is an attempt at EN 60204-1 compliance as the 24V d.c. wiring is blue.

 

[Bobster]

Following 60204 they've used the colour allocated to I.S wiring.

Those don't look like terminals, more like slim line relays. Maybe used to interpose between the PLC and the field device.

 

[netblindpaul]

Where in 60204 does it deal with intrinsically safe equipment Rob?

It's not in the copy I have which is the last harmonised issue according to the EU website against the MD.

Intrinsically safe equipment is not dealt with in 60204 at all as far as I can tell.

The only thing you could argue is that the colour blue is light, or unsaturated, suggesting that it is a neutral conductor.
I would not like to say either way due to it being a picture on a website!

Further than that colour wise and you would have to go to EN 60446.

I would love to be enlightened as to where IS wiring colours are specified in 60204 because I can't find it, & I've just spent the last few days on a CE marking assessment report for a machine, so I've been living and breathing EN standards!

As far as the relays thing goes, you are almost certainly right, my eyes are not good enough!

 

[Bobster]

Correct it's not in 60204.

It is left out deliberately because its recomended in the hazardous area standard. (Can't remember the number off the top of my head)