Why Quarter Turns?

Why Quarter Turns?

Some Backstory

In the mid 20th century electrical switchboard cabinet manufacturing processes were not standardised in any way. Most cabinets were manufactured using repurposed parts from other industries and components were welded with no thought given to upkeep or replacement of worn parts. T and L handles became popular as the locking component for cabinets but, as production of electrical switchboard cabinets increased, the amount of time spent installing T and L handles became a costly issue.

Who Invented Quarter Turn Locks?

In the late 60’s an inspiring German toolmaker, Dieter Ramsauer, recognised the problems within the electrical switchboard market and endeavored to develop a modular quarter turn that reduced assembly time and standardised the cutout size. Dieter Ramsauer would later go on to start the Dieter Ramsauer Konstruktionselemente GmbH aka Dirak.

The Immediate Benefits Of Using A Quarter Turn Lock

T and L handles require 3 holes in the sheet metal, two for screws to secure the handle and one for the shaft, which the cam is attached to. It also means that the cam has to be fitted after the handle has been inserted. In comparison, quarter turns can be inserted complete with their cam through the front face and just need a nut to be tightened to secure them to the panel. The quantity of steps, tools and fine motor skills involved in using the T and L handles in assembly requires more effort and time over the simpler methodology of the quarter turns.

Key Features Of Quarter Turns

Modern quarter turns have a variety of ingenious features for their size.

What is a Grounding Nut?

Most quarter turns have small teeth on the nut used to secure the quarter turn to the panel. These teeth slightly dig into the sheet metal panel ensuring the quarter turn is grounded to the panel. These are known as a grounding nut and are a necessity when using quarter turns for electrical switchboard cabinets.

When to use an 8mm Square (or Triangle) insert or a 7mm Square (or Triangle) insert

Quarter Turn 7mm 8mm Inserts

Quarter turns have inserts that generally come in two sizes. These size differences are intentional and not part of some sort of preference. The idea behind them is that the 8mm size insert is used on high voltage cabinets, the 7mm size insert is used on low voltage cabinets. Not all electricians are licensed to work in high voltage cabinets, they are given 7mm size keys and these keys will not physically fit in the 8mm insert. Conversely, those electricians with high voltage licenses are given an 8mm size key that will work with 8mm inserts and 7mm inserts.

What are the purposes of the different shape inserts?

Quarter Turn insert types

Other than the square or triangle inserts there are also double bit, 2x4 slotted, slotted square, wing knob, keylockable and padlockable (there are some other shapes too, but these are the common ones). These all give varying degrees of security. A wing knob allows for easy and ergonomic access with no restriction. A slotted 2x4 insert can be opened with either a coin or a screwdriver, not secure, but a small deterrent from wandering hands. The slotted square gives the same amount of security as the slotted 2x4 (that is, no real security) but allows electricians to use their normal square keys that are used for electrical cabinets. The 3mm and 5mm double bits function the same as the 7mm and 8mm inserts but are designed to be harder to open with a set of pliers. The most secure quarter turns would either be keylockable or padlockable meaning a key is needed to gain access.

Why do the cams have bent corners?

Metal Cam With Bent Corners

The metal cams used in standard quarter turns are bent at the corners. This allows the quarter turn to enact about 3mm of compression to secure the door against the rubber gasket. Meaning the door has a better seal and is more likely to stop the ingress of dirt, dust and water.

Why is the cutout octagonal?

Octagonal Cut Out for Quarter Turns

The octagonal cutout is designed to allow the quarter turn to be inserted from the front of the panel whilst the cam is attached. Using a circular hole means the quarter turn would freely spin. Some electrical switchboard cabinet manufacturers will use a square hole.
Manufacturers that use a square cutout instead need to pay attention to what size escutcheon (the collar of the quarter turn on the front face of the panel) quarter turns they are using. A common escutcheon size is 32mm and it will cover the extra hole size of the square compared to the octagonal, but a 28mm escutcheon, which is equally as common, will not cover the extra. Whilst it won’t be detrimental to the functionality of the quarter turn it is aesthetically not pleasing and will affect the IP rating of the whole cabinet.

Quarter turn locks are designed to be at least IP65 rated.


Due to the inherent design features of the quarter turn, when properly installed they are at least IP65 rated. This means they are maximum rated against ingress of dust and provide protection from low pressure water from all practical directions. Essentially they are weatherproof but not suitable for submerged applications or high pressure cleaning.

Why are they called Quarter Turn Latches (or Locks)?

Quarter Turn highlighting inset causing 90 degree rotation

They, unsurprisingly, rotate the cam a quarter of a turn or 90 degrees to open or close. This function can be achieved in two different ways. There can be a rotational limiting function inside the quarter turn housing, these function with a cam without a stopper. More commonly, rotational limiting is external to the quarter turn housing. An inset of the outside of the housing allows a stopper from a cam to sit in it, this stopper is limited by the length of the inset.

How to make sure the cam you pick is the correct size for your quarter turn.

Example of Positive cam height

The quarter turn latches onto the return of the cabinet at a specific depth. This dimension is known as the H dimension. This H dimension is measured as the underside of the escutcheon to the top face of the cam. Likewise, to measure what H dimension is required for any given cabinet you would need to measure from the outside face of the cabinet (material thickness needs to be included) to the top face of the return the latch fits onto.
Common convention when selecting cams is that the H dimension is included in the part number. For example, if a 28mm H dimension is needed, the part number would be an MCAM-28.
There is a rather important caveat though. The H dimensions that form the part number are based off a standard size quarter turn housing which is 18mm. This means an MCAM-18 would be a flat cam as it includes the 18mm that a standard size quarter turn housing contains. An MCAM-28 has a 10mm offset, so when it is used with a standard size quarter turn housing of 18mm it creates an H dimension of 28mm.

Quarter Turn with 20mm housing
This means if a non-standard size quarter turn is used, it needs to be remembered that the part numbers for cams revolve around a standard cam size. For example, if there is a non-standard size housing of 20mm and the desired H dimension is 18mm an MCAM-16 would need to be used as it has a -2mm offset (that is because a standard housing is 18mm, to make a H dimension of 16mm would require a -2mm offset).

The total height from the underside of the escutcheon to the top of the cam is the H dimension.
The offset of a cam is sometimes referred to as the CH dimension.

The housing size is sometimes referred to as the LH dimension.
The L or CL dimension is the length of the cam measured from the hole center to the end of the cam, a standard L dimension is 45mm.

If you are unsure what size cam you need, contact Selectlok on 03 8318 4900 and let us know what style quarter turn you're wanting to purchase, what H dimension you need and we will work out what cam size you need.

Some Quarter Turn Latches Are Spring Loaded

A spring loaded quarter turn lock has a spring added into the locking mechanism that will return the mechanism to the locked position. It might not seem like much but, unlike normal locking mechanisms with pins or wafers, quarter turns with shaped inserts allow for the key to be removed at any point during the process.

When Compression Is A Must

Compression Quarter Turn Technical Drawing

When a cabinet requires a certain amount of compression a compression quarter turn lock should be used. These quarter turn locks will rotate the latch with one 90degree turn of the key, and then bring the latch towards the door pulling it in tight. Our quarter turns enact 7mm of compression.

Now You're More Informed, You Can Make The Right Choice

And the right choice is always Selectlok!

We have a wide range of quarter turn locks and quarter turn latches. Selectlok has been supplying hardware to the electrical switchboard industry since 1986.

Click here to check out our Quarter Turn Lock range

Click here to check out our marine grade Stainless Steel 316 Quarter Turn Locks

Click here to check out our Padlockable Wing Knobs