degrees of protection against impact

[Greg:]

I'm wondering about the use of J in impact related regs?

Here's an example of its use in the BRB:
705.522.16 Conduit systems, cable trunking systems and cable ducting
…
(i) conduits shall provide a degree of protection against impact of 5 J according to BS EN 61386-21
(ii) cable trunking and ducting systems shall provide a degree of protection against impact of 5 J according to BS EN 50085-2-1.

Here's my problem. Joules (in mechanics) are used to measure forceful movement through a distance but, from the perspective of a piece of containment, seems to me that their would be a big difference if that force was delivered through something sharp (such as the blade of an axe) or something blunt (with a surface not dissimilar to the side of the axe).
Similarly, an object with the effect of a fast moving hammer could have a deep localised impact while a slow moving vehicle could cause a shallower impact across a wide area through the delivery of a similar quantity of energy.

There's no reference to J in the symbols section of part 2 so it seems to me that SI defaults are in use here. It all leaves me wondering: how J related impact regs are applied in practice, why a pressure related measure wasn't used and how the use of J is explained elsewhere in the regs and other BS documents.

thanks

 

[Engineer54]

Impact is the 3rd number on the IP system tables. The impact figures when given, are based on a given measurable lab test, similar to the official finger measurement used in the other IP rating.... Impact resistance/value is rarely seen or given, even when IP tables are shown in publications. It would be nigh on impossible to cover every impact type and situation, in the real world, let alone trying to guard against them all!!

 

[ackbarthestar]

Impact resistance/value is rarely seen or given, even when IP tables are shown in publications

I suspect the reason why IP ratings for mechanical protection are not usually present is that in Europe, the IK values have superseded them. Although, reading them it is difficult to transpose the laboratory (UKAS) results into everyday application unless explicitly stated on accessory being installed.

 

[Greg:]

Thanks for that. It makes me even more curious about the J reference though.


The third digit of the IP codes turns out to refer to Joules but not directly to the number of Joules involved


IP Third number - Protection against mechanical impacts (commonly omitted, the third number is not a part of IEC 60529)
0 No protection.
1 Protects against impact of 0.225 joule
(e.g. 150 g weight falling from 15 cm height).
2 Protected against impact of 0.375 joule
(e.g. 250 g weight falling from 15 cm height).
3 Protected against impact of 0.5 joule
(e.g. 250 g weight falling from 20 cm height).
4 Protected against impact of 2.0 joule
(e.g. 500 g weight falling from 40 cm height).
5 Protected against impact of 6.0 joule
(e.g. 1.5 kg weight falling from 40 cm height).
6 Protected against impact of 20.0 joule
(e.g. 5 kg weight falling from 40 cm height).
sources: IP - Ingress Protection Ratings engineeringtoolbox.com
also Tyro Industrial Remote Control Systems - IP (Ingress Protection) tyroremotes.co.uk
(the rarity of pages supplying this info confirms your "when given" comment).


I'm still left wondering what 5 J means. I wouldn't have thought that 5 J would be a direct reference to the third IP number which would translate to 6 Joules.

 

[ackbarthestar]

I'm still left wondering what 5 J means. I wouldn't have thought that 5 J would be a direct reference to the third IP number which would translate to 6 Joules.

IK 0 - 8 doesn't necessarily translate into Joules.

But given the parameters of the IK code and test you can get a fairly accurate answer in Joules

WD = Mass * acceleration * Distance (Joules)

 

[Greg:]

Excellent. The plot thickens.


Why have one set of codes when you can have two!


Judging on numbers displayed for google search results, IK codes are have less currency than IP codes and they work like this.


Standard IEC 62262 defines an IK code that characterises the aptitude of equipment to resist mechanical impacts on all sides (see Fig. E49).
IK code Impact energy (In joules) AG Code
00 0
01 = 0.14
02 = 0.20 AG1
03 = 0.35
04 = 0.50
05 = 0.70
06 = 1
07 = 2 AG2
08 = 5 AG3
09 = 10
10 = 20 AG4
source: Protection provided for enclosed equipment: codes IP and IK - Electrical Installation Guide Main Page - Electrical Installation Guide


Oh great there's also an AG code.


So you might get IPXX5, IK05 and perhaps "Agsomething" as well.


Still wondering about 5 J?

No reference was made to IP, IK, AG or anything else - just J.

 

[Greg:]

twice in one reg

where's my axe and hammers?

 

[Knobhead]

I’ve been following this thread with interest. Being “industrial” I’d like to add a new factor in to the equation. I’ll apologise now I am taking the Mickey here, I would proposes a new impact resistance measurement to the BS codes, the “Ivan”. The protection given by a Chieftain tank would come to about 0.7 on the Ivan scale. A small shed with 8 X 12 RSJ’s as the frame clad in double skin 5/8th cross grained plate would be about 0.4 Ivan’s. Ivan was a guy I had to contend with at work. You could design a control station to be bomb proof, he’d bend it just by looking at it. He was moved from job to job in the hope of finding something he couldn’t break, he had to go in the end. I installed a new control station, in a steel shed, he wrecked it by driving over it with a 70 tonne loader. The paint hadn’t even bloody dried!

 

[mayfair]

Tony check your pm's ta

I’ve been following this thread with interest. Being “industrial” I’d like to add a new factor in to the equation. I’ll apologise now I am taking the Mickey here, I would proposes a new impact resistance measurement to the BS codes, the “Ivan”. The protection given by a Chieftain tank would come to about 0.7 on the Ivan scale. A small shed with 8 X 12 RSJ’s as the frame clad in double skin 5/8th cross grained plate would be about 0.4 Ivan’s. Ivan was a guy I had to contend with at work. You could design a control station to be bomb proof, he’d bend it just by looking at it. He was moved from job to job in the hope of finding something he couldn’t break, he had to go in the end. I installed a new control station, in a steel shed, he wrecked it by driving over it with a 70 tonne loader. The paint hadn’t even bloody dried!

 

[Knobhead]

Tony check your pm's ta

I would do if I could.

 

[Greg:]

I would proposes a new impact resistance measurement to the BS codes, the “Ivan”. The protection given by a Chieftain tank would come to about 0.7 on the Ivan scale. A small shed with 8 X 12 RSJ’s as the frame clad in double skin 5/8th cross grained plate would be about 0.4 Ivan’s.

Just drop the two "abouts", specify locations on both tank and shed and we'd then have a usable scale presuming both tank and shed were tested while in mint condition.


I guess clarity might even be given to the 5 J reg references.


Engineeringtoolbox.com made their explanation of IP third digits to say:

IPXX4 protects an against impact of 2.0 joule
(e.g. 500 g weight falling from 40 cm height).

Similarly 5 Joules of energy gets delivered by:
1 kg weight falling half a metre.
(similar result as a 1.25 kg weight falling 40 cm)

However, lacking clarity about how sharp the impacting object may be, the regs, IP and IK references still lack the strengths of Tony's scale.

With no better proposal, my vote's for Ivan.