technical article - mcb lockouts · tim hughes – tech iosh total lockout (safety) ltd braintree...

Technical Ar cle Product Focus - MCB Lockouts

Copyright © 2011: Total Lockout (Safety) Ltd Tel: +44 (0)1376 325506

Introduc on:

There are hundreds of diff erent makes and model of Miniature Circuit Breakers (MCB) on the market. Choosing the right lockout device can seem daun ng. With the guidance provided in this ar cle, and reference to our selec on guide, the choice is made much simpler. With a well fi ed MCB lockout, secured in place with a safety padlock, workers are protected against the risk of unexpected start-up or energiza on of the electrical circuit.

Preamble

This product focus relates only to low voltage breakers; the type that you might fi nd in a domes c or commercial consumer unit which clip on to a standard DIN rail. There are many other breaker types on the market which grow in size as the voltage increases. These large breaker lockouts are not included in this ar cle.

Lockout Types

In this ar cle we make a comparison between the MCB lockouts manufactured by Brady and Master Lock. There are four diff erent versions from each manufacturer each designed to fi t the same range of breakers. These are illustrated below.

Given the applica on similari es of these devices, choice is o en made simply on price alone. Indeed there is quite a contrast in price with the Brady versions cos ng more than twice that of the Master Lock versions. This ar cle aims to provide an objec ve comparison which highlights the various features and gives the authors opinion of the price variance.

Func on

The fi rst three devices in each range work by engaging wire pins into small holes located either side of the MCB switch toggle.

Brady POS(Pin Out Standard)

Brady POW(Pin Out Wide)

Brady PIS(Pin In Standard)

Brady TBLO(Tie Bar Lock Out)

Master Lock S2391Master Lock S2390 Master Lock S2392 Master Lock S2393



In order to engage the pins into the holes, they have to be exposed further. On the Brady version, this is achieved by pressing the spring loaded plunger with the thumb. On the Master Lock version, the two halves of the lockout device hinge apart. See Figures 3 & 4.

Having exposed the wire pins in this way, they can now be manipulated into the engagement holes on the breaker. This is fi ddly task on both versions and requires some dexterity. However, once the task has been successfully completed, one can quickly gain ‘the knack’ making subsequent a empts quite straight forward.

Once fi ed, the padlock can be easily added. On the Brady version, the spring loaded plunger retracts exposing the padlock hole. On the Master Lock version, the two halves must be hinged together to align the padlock holes.

The padlock hole diameter on the Brady version is 7.35mm, on the Master Lock version is it 7.9mm. Given that most safety lockout padlocks have a shackle diameter between 5mm and 6.5mm, both are perfectly adequate.

Engagement holes

Lockout pins

Figure 1 - Brady MCB Lockout

Engagement holes

Lockout pins

Figure 2 - Master Lock MCB Lockout

Figure 3 - Brady MCB LockoutFigure 4 - Master Lock MCB Lockout



The second versions in each range (Master Lock S2391 and Brady POW) are designed to fi t on MCB breaker toggles with a wider engagement hole se ng. However on the Master Lock version the width of the wire pins is only marginally wider than their other version S2390; on that note it’s less obvious that these two (S2390 and S2391) are diff erent. To compensate for this, the la er has a red thumb pad, whereas the former is black.

The third versions in each range (Master Lock S2392 and Brady PIS) are designed to fi t on MCB’s where the engagement holes are inset from the edge of the breaker.

The fourth versions in each range (Master Lock S2393 and Brady TBLO) off er a degree of universality. Both can be used on mul -pole breakers which are operated with a e-bar. The Master Lock version can also be used as a subs tute for the other versions in the range, giving wider appeal. You could eff ec vely use this version alone for most MCB’s; this capability is not possible with Brady’s TBLO device. The Master Lock version is fi xed to the breaker using a small screw driver which drives a pointed grub-screw into the breaker toggle crea ng a small indenta on. Repeated a achment to the same breaker may cause damage, eventually preven ng the lockout from a aching.

Build Quality

Overall, the Brady version feels be er made. In their literature Brady state that their MCB lockouts are made from glass-fi lled nylon. Master Lock does not state the material of manufacture in their literature although the plas c does ‘feel’ more fragile.

Fit for purpose

When fi ed to the MCB, a small amount of force could be used to tear either device from the breaker. However in doing so, both manufacturers’ products remain undamaged. Damage occurs to the breaker itself with the engagement holes being split open. On this point a en on is drawn to Sec on 8 of The Health & Safety at Work etc. Act 1974 which “Places a duty on everyone not to inten onally or recklessly interfere with or misuse anything provided in the interests of health, safety and welfare”. Individuals contempla ng such ac on to override a lockout, should be mindful of this and not only the legal consequences but also the personal ones.

Conclusions

In all cases, each lockout from both manufacturers was found to fi t to the MCB’s for which they are specifi ed. All perform the func on for which they are designed. As previously men oned, Master Lock’s S2393 off ers some universality, poten ally nega ng the need for some of the others in the range. That said, it may not fi t quite so well as others which are specifi cally designed for their host MCB although this aspect has not been fully assessed in this comparison.

The Brady versions are of be er quality manufacture and feel more ergonomic. They are marginally easier to fi t on the MCB than the equivalent Master Lock equivalent.

Despite all this, at less than half the cost of the Brady range, Master Lock’s MCB lockouts are perfectly fi t for purpose. The occasional breakage is tolerable given the cost saving available.

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About the author.

For 25 years, Tim Hughes has held design, project management and technical sales roles in the process and machinery safety industries.

He worked for valve interlock systems manufacturer Smith Flow Control in the late 1980’s. In 1990 he designed the Prosafe mechanical interlock but returned to Smith Flow Control in 1993. From 1996 to 1998 he was assigned to Smith’s offi ce in Singapore where he helped develop their market posi on in South East Asia. In 2001 Tim joined machinery interlock manufacturer Castell Safety Interna onal, ini ally as Business Unit Manager for Iso-lok, Castell’s range of lockout tagout equipment. A er a short spell with Master Lock in 2009/10, Tim started his own company Total Lockout (Safety) Ltd as a distributor of lockout tagout products.

Tim Hughes – Tech IOSHTotal Lockout (Safety) LtdBraintreeEssexCM77 8XWUnited Kingdom

[email protected]

technical article - mcb lockouts · tim hughes – tech iosh total lockout (safety) ltd braintree...

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