The latest news from the Unipart Rail Group of Companies

The Delights of the DLIT

The Delights of the DLIT

The Solid-State Interlocking (SSI) Data Link Isolating Transfer (DLIT) is used to isolate sections of the SSI data link, in order to limit levels of induced common mode interference.

Electrified railways are well known to present various issues and problems regarding Electro Magnetic Interference (EMI). In 25 kV AC railway electrified areas, it has been best practice to use the traction return earths rather than separate earth systems. The effect of 50 Hz interference can degrade the components of the surge protection units (SPUs) installed to protect the SSI data link, due to constant stress, thus rendering them less effective as protection devices, and cause potential problems with data corruption. 

The current practice is to install DLIT’s to restrict common-mode voltages and reduce the propagation of transients. Where older installations do not have these devices, retrospective upgrades should be considered. A word of warning is to check the current operation of each data link against the original design and ensure the installation of each DLIT does not exacerbate any existing design or maintenance defects.  It should also be noted that in longer base band data links where repeaters are used, each DLIT added reduces the maximum permitted length of the data link.

The DLIT must be used in accordance with Network Rail SSI8503, Issue 04, SSI Applications Manual, Earthing and Bonding of Solid-State Interlocking Equipment.

The Network Rail Certificate of Acceptance reference for the DLIT is PA05/02963.

The Network Rail catalogue number for the DLIT is 0086/069367 and for the DLIT Housing, 0086/069368.


Click here For more information on DLIT and other products from Park Signalling.

If you have a specific enquiry please contact us:


Delivering Value through Product Innovation and Increased Performance   




About this author
Nicola Holt

Infrastructure Marketing Manager

I have been a part of the Unipart Rail marketing team for over 15 years in the role as Marketing Manager. I focus mostly on supporting the Signalling side of the business with Unipart Dorman, in the UK and North America and also our more recent acquisition - Park Signalling. The Unipart Dorman Traffic sector is also a key area in which I support in addition to the Unipart Rail Manufacturing business.


Leave a Comment

Name (required):

Email (Will not be published) (required):

Your thoughts: (Characters remaining: ) )

SPAM Protection: Sum of 13 + 5 ?

Read the Ts & Cs? Tick to confirm you agree to abide by our house rules

Enter text shown in this image into the box below.

Search Our Blogs

Recent Tweets

Commenting Guidelines
By commenting on this blog you agree to abide by our Terms and Conditions. Although we will do our utmost to avoid it, we reserve the right to edit, move or delete any comments which do not follow the guidelines provided