# PTP boundary-clock interface Canonical URL: https://eloragrid.ai/symbols/ptp-boundary-clock-interface Publisher: Elora Grid Updated: 2026-11-03 Lookup label: PBI Drawing use: Schematic Reference families: Manufacturer Representation: Functional block Installation focus: substations Input: Upstream PTP reference Output: Downstream timing distribution Shows the timing boundary provided by a selected network clock between its upstream and downstream segments. ## In plain English ### What this block does Shows the timing boundary provided by a selected network clock between its upstream and downstream segments. ### A simple example In a substation, a station clock can provide precision timing to process equipment and another timing interface to event recorders. The alarm system should distinguish loss of a distribution path from loss of the external time source. For this reference, the drawing identifies “Upstream PTP reference” at the input and “Downstream timing distribution” at the output. Network clock role is configuration-specific. ### What the drawings help you do Start at the named input: Upstream PTP reference. Identify its source device or document and the state represented on the drawing. Follow the named output: Downstream timing distribution. Cross-reference its destination and separate the command from confirmation that the equipment responded. ### Terms - Input: Upstream PTP reference - Output: Downstream timing distribution - Application reference: An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections. Concept diagram: Upstream PTP reference → PBI → Downstream timing distribution A reading guide. The entry's original illustration and input/output facts describe this application. - [SEL-2488 satellite-synchronised network clock](https://selinc.com/products/2488/) ## What it represents Shows the timing boundary provided by a selected network clock between its upstream and downstream segments. A station time system provides a shared time reference for protection records, measurements and automation. Different devices can use different timing protocols, so the time source, distribution path and quality information must remain identifiable. In a substation, a station clock can provide precision timing to process equipment and another timing interface to event recorders. The alarm system should distinguish loss of a distribution path from loss of the external time source. For this reference, the drawing identifies “Upstream PTP reference” at the input and “Downstream timing distribution” at the output. Network clock role is configuration-specific. Show the source and client of each time connection. Required accuracy, holdover, protocol profile and loss-of-time behavior follow the selected application; a common timestamp format does not guarantee synchronized events. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation. ## How to read it - Start at the named input: Upstream PTP reference. Identify its source device or document and the state represented on the drawing. - Follow the named output: Downstream timing distribution. Cross-reference its destination and separate the command from confirmation that the equipment responded. - Network clock role is configuration-specific. - Show the source and client of each time connection. Required accuracy, holdover, protocol profile and loss-of-time behavior follow the selected application; a common timestamp format does not guarantee synchronized events. ## Information to show or reference - Label the source and connection reference for upstream ptp reference. - Identify the destination and defined state of downstream timing distribution. - Record the equipment or control-document revision supporting this functional block. - Check this application limit in the project design: Network clock role is configuration-specific. ## Important distinction Network clock role is configuration-specific. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram. ## Facts - Representation: Functional block - Installation focus: Substations - Input / boundary: Upstream PTP reference - Output / connection: Downstream timing distribution - Lookup label: PBI is a library lookup label, not a standard device designation. ## Public references - [SEL-2488 satellite-synchronised network clock](https://selinc.com/products/2488/) — SEL. Public technical context for substation timing and event interfaces. PTP, NTP, IRIG-B, pulse distribution, reference failover and timing quality. The application text and educational graphic are independently authored; the publisher does not certify this representation. ## Graphic scope Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.