Why are 30mm push buttons installed from the back?
Credit to Author: Jeremy Calluaud| Date: Mon, 22 Jul 2019 13:13:44 +0000
Today, the main standard for pushbuttons is to be installed on 22mm cut out with a product mounting from the front of the panel. Nevertheless, another important standard is the installation on 30mm cut out with an implementation of products from the back of the panel. This standard which remain for many decades present several benefits over the 22mm products.
- A flat gasket could seal over a larger surface area from the back than we are able to from the front.
- Notches were provided in the 30mm cut out to ensure that the pushbuttons would not turn when operated and this is especially important for selector switches. Since the devices were designed for industrial use (such as automotive and machine tool segments) the personnel operating the machinery were known to be rough on the equipment, so customers wanted devices to withstand the physical environment and the abuse of the personnel. Customers did not want the push buttons nor selector switches to rotate when being used hard. These notches are also used for aligning legend plates.
- Because of the notches, the sealing gaskets were able to seal better and easier from the back.
- Customers did not need to concern themselves with what to put on the front of the panel (i.e.: legend plates, lockouts, guards) because the sealing was from the back. No need to worry if the enclosure rating was maintained if they used a lockout with a guard and a nameplate – the devices maintained their enclosure rating.
- End users wanted an easy way to keep the operators tight without having to open the panel. One reason is arc flash. Another reason is that Unions are very strong in USA at end uses, and they enforce many rules themselves. In most facilities, the only person who can open an electrical enclosure or panel is an electrician. The only person who can tighten devices up or secure mechanical things is a machinist (a push button is a mechanical device when the contact block is an electrical part). An electrician belongs to one union group while the machinists belong to a different union group and neither one is allowed to the other person’s work. So, if a push button installs from the front (and then, is tightened up on the back), you would need two trade unions to be present: an electrician to open and close the panel and a machinist to tighten up the push button or selector switch. Therefore, two highly paid union personnel would need to go to the panel and wait on each other to tighten up a push button. So, with a mounting from the back and with the notch to hold the operator in place, only one machinist would be needed to come and tighten up a loose push button from the front. The octagonal ring nut makes it easy to tighten an operator from the front.
- Mounting the push button from the back with multiple compensating gaskets was a good way to counter balance for varying enclosure thicknesses: from a thin sheet metal enclosure to a thick case of aluminum or zinc enclosures by way of stainless steel or plastic enclosures. Mounting our 30mm push buttons is simple and easy, while keeping the same enclosure ratings. For information, panel or enclosure thickness can vary from 1,6 to 6,4 mm (0,6 to 0,25 inches).
- Changing the lamp, whether incandescent, neon or LED, is possible from the front of the operator without opening the panel. This is especially helpful with today’s growing concern over arc flash.
- All the major US suppliers of 30mm push buttons use a similar mounting method from the back and it has become the industry standard since around World War II. This main standard in North America is a tried and true solution over the years and up to now.
- Because the contact blocks can be fixed directly on the operator devices and without any fixing collars, there is less part number to order and to stock for distributors (head operator + contact blocks for 30mm vs. head operator + fixing collar + contact blocks for 22mm). And the mounting process is simplified.
If those benefits raised your interest and if you want to know more about this offer, you can discover it in detail on our Schneider Electric website at https://www.schneider-electric.com/en/product-range/634-harmony-9001-k/?filter=business-1-industrial-automation-and-control (metal offer) and/or https://www.schneider-electric.com/en/product-range/1858-harmony-9001sk/?filter=business-1-industrial-automation-and-control. (plastic offer)
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